diff --git a/lib/importer/src/dudk/backend.js b/lib/importer/src/dudk/backend.js
index fa6b85de..83cf80ef 100644
--- a/lib/importer/src/dudk/backend.js
+++ b/lib/importer/src/dudk/backend.js
@@ -5,6 +5,7 @@ const attributeTypes = require('./types/attribute-types');
 const guesser = require('./types/guesser');
 const store = require("./session_store")
 const errorTypes = require('./util/errors');
+const Range = require('./util/range');
 
 // An implementation of the interface described in https://struct.register-dynamics.co.uk/trac/wiki/DataImporter/API
 
@@ -78,13 +79,12 @@ exports.SessionGetSheets = (sid) => {
 exports.SessionSetHeaderRange = (sid, range) => {
   assert(range != null, "Null range passed to SessionSetHeaderRange");
   assert(range.sheet != null, "Range with null sheet passed to SessionSetHeaderRange");
-
   sessionStore.apply(sid, (s) => { s.headerRanges[range.sheet] = range; })
 };
 
 exports.SessionGetHeaderRange = (sid, sheetName) => {
   let session = sessionStore.get(sid);
-  return session.headerRanges[sheetName]
+  return session.headerRanges[sheetName];
 };
 
 exports.SessionSetFooterRange = (sid, range) => {
@@ -95,7 +95,7 @@ exports.SessionSetFooterRange = (sid, range) => {
 
 exports.SessionGetFooterRange = (sid, sheetName) => {
   let session = sessionStore.get(sid);
-  return session.footerRanges[sheetName]
+  return session.footerRanges[sheetName];
 };
 
 function getDimensions(sid) {
@@ -237,46 +237,28 @@ exports.SessionSuggestDataRange = (sid, headerRange, footerRange) => {
       // the header.
 
       // Header and footer, so just go from the row below the header to the row above the footer
-      return {
-        sheet: sheetName,
-        start: {
-          row: headerRange.start.row + 1,
-          column: headerRange.start.column
-        },
-        end: {
-          row: footerRange.start.row,
-          column: headerRange.end.column
-        }
-      };
+      return new Range(
+        sheetName,
+        { row: headerRange.start.row + 1, column: headerRange.start.column },
+        { row: footerRange.start.row, column: headerRange.end.column }
+      );
     } else {
       // Header, but no footer, so just go from the row below the header to the end
-      return {
-        sheet: sheetName,
-        start: {
-          row: headerRange.start.row + 1,
-          column: headerRange.start.column
-        },
-        end: {
-          row: sheetDimensions.rows - 1,
-          column: headerRange.end.column
-        }
-      };
+      return new Range(
+        sheetName,
+        { row: headerRange.start.row + 1, column: headerRange.start.column },
+        { row: sheetDimensions.rows - 1, column: headerRange.end.column }
+      );
     }
   } else {
     // No header range specified, so take all but the first row of the first sheet
     const sheetName = sessionStore.get(sid).sheetNames[0]; // Find the first sheet
     const sheetDimensions = dimensions.sheetDimensions.get(sheetName);
-    return {
-      sheet: sheetName,
-      start: {
-        row: 1,
-        column: 0
-      },
-      end: {
-        row: sheetDimensions.rows - 1,
-        column: sheetDimensions.columns - 1
-      }
-    };
+    return new Range(
+      sheetName,
+      { row: 1, column: 0 },
+      { row: sheetDimensions.rows - 1, column: sheetDimensions.columns - 1 }
+    );
   }
 }
 
@@ -375,7 +357,8 @@ function cellsToSamples(row) {
   return row.map(cellToSample);
 }
 
-// Returns a sample of rows in a range. range is of the form {sheet: 'Foo', start:{row: X, column: Y}, end:{row: X, column: Y}}.
+// Returns a sample of rows in a range. range is and instance of the Range class and
+// is of the form {sheet: 'Foo', start:{row: X, column: Y}, end:{row: X, column: Y}}.
 
 // Returns three arrays - one with startCount rows from the top of the range,
 // one with a random selectino of middleCount rows from the middle, and another
@@ -385,7 +368,8 @@ function cellsToSamples(row) {
 exports.SessionGetInputSampleRows = (sid, range, startCount, middleCount, endCount) => {
   assert(range != null, "Null range passed to SessionGetInputSampleRows");
   assert(sessionStore.has(sid), `No such session ${sid} when getting input sample rows`);
-  assert(sessionStore.get(sid).wb.Sheets[range.sheet], `No such sheet ${range.sheet} in session ${sid} when getting input sample rows`);
+  assert(sessionStore.get(sid).wb.Sheets[range.sheet], `No such sheet ${range.sheet} in session ${sid} when getting input values`);
+
   if (range.end.row < range.start.row || range.end.column < range.start.column) {
     // Range is empty
     return [[], [], []];
@@ -393,7 +377,6 @@ exports.SessionGetInputSampleRows = (sid, range, startCount, middleCount, endCou
   // If the caller asked for more rows than we have, or if the start/middle/end would overlap, clamp the counts
   const totalRowsInRange = (range.end.row - range.start.row + 1);
   [startCount, middleCount, endCount] = clampCounts(startCount, middleCount, endCount, totalRowsInRange);
-
   const sheet = sessionStore.get(sid).wb.Sheets[range.sheet];
   const data = sheet["!data"];
   const merges = sheet["!merges"];
@@ -418,7 +401,6 @@ exports.SessionGetInputSampleRows = (sid, range, startCount, middleCount, endCou
   let endRows = extractColsFromRows(getMergedRows(sheet, range.end.row - endCount + 1, range.end.row),
     range.start.column, range.end.column + 1);
 
-
   // Given an index generate a function that we can use to map across an array to turn it into
   // an object with both index and the array data.
   const mapWithIndex = (arr, startIndex) => {
@@ -430,12 +412,6 @@ exports.SessionGetInputSampleRows = (sid, range, startCount, middleCount, endCou
     }
   }
 
-  // FIXME: Work out how the xlsx library represents styles and
-  // rowspan/colspan and make sure that what we return does something useful
-  // with that information. We DO want styling information to be available in
-  // the preview, so that users can see their spreadsheet in a more familiar
-  // form, and because styling information might be a significant part of the
-  // data.
   return [
     startRows.map(mapWithIndex(startRows, range.start.row)),
     middleRows.map(mapWithIndex(middleRows, middleStart)),
@@ -532,8 +508,8 @@ exports.SessionGuessTypes = (sid, range) => {
 // objects with string fields "displayName" and "description", and an optional Map
 // field "formats" that maps from format names (as returned by SessionGetTypes)
 // to objects with strings field "displayName" and "description".
-exports.SessionGetSupportedTypes = (sid) => {
-  return types.supportedTypes;
+exports.SessionGetSupportedTypes = (_sid) => {
+  return attributeTypes.supportedTypes;
 };
 
 // Given guesses as returned by SessionGuessTypes and a list of domain-model
@@ -573,8 +549,7 @@ exports.SessionSuggestFields = (sid, typeGuesses, domainModelFields) => {
 exports.SessionGetInputValues = (sid, range, maxValues) => {
   assert(sessionStore.get(sid), `No such session ${sid} when getting input values`);
   assert(sessionStore.get(sid).wb.Sheets[range.sheet], `No such sheet ${range.sheet} in session ${sid} when getting input values`);
-  assert(range.end.row >= range.start.row, `End row (${range.end.row}) must be >= start row (${range.start.row}) to get input values`);
-  assert(range.end.column >= range.start.column, `End column (${range.end.column}) must be >= start column (${range.start.column}) to get input values`);
+  assert(range.isValid(), `Range is invalid: end (${JSON.stringify(range.end)}) must be >= start (${JSON.stringify(range.start)}) to get input values`);
 
   const sheet = sessionStore.get(sid).wb.Sheets[range.sheet];
   const data = sheet["!data"];
@@ -679,7 +654,7 @@ exports.SessionPerformMappingJob = (sid, range, mapping, includeErrorRow = false
   validateMapping(range, mapping);
 
   const records = new Array(); // Array of output records
-  const errors = new Array();;
+  const errors = new Array();
   const warnings = new Array();
 
   const sheet = sessionStore.get(sid).wb.Sheets[range.sheet];
@@ -688,15 +663,14 @@ exports.SessionPerformMappingJob = (sid, range, mapping, includeErrorRow = false
   const attrMap = Object.entries(mapping.attributeMappings);
   const attrTypes = mapping.attributeTypes || {};
 
-
-  // TODO: Replace this with a map/sum once range is a real type.
+  // Use Range.applyRows to determine expectedColumnCount
   let expectedColumnCount = 0;
-  for (let rowIdx = range.start.row; rowIdx <= range.end.row; rowIdx++) {
+  range.applyRows((rowIdx) => {
     let row = getMergedRow(data, merges, rowIdx);
     if (row && row.length > expectedColumnCount) expectedColumnCount = row.length;
-  }
+  });
 
-  for (let rowIdx = range.start.row; rowIdx <= range.end.row; rowIdx++) {
+  range.applyRows((rowIdx) => {
     let rowErrorCount = 0;
     let row = getMergedRow(data, merges, rowIdx);
     let recordCells = {};
@@ -706,7 +680,7 @@ exports.SessionPerformMappingJob = (sid, range, mapping, includeErrorRow = false
       // Ensure we exclude footer rows from the validation as they may not
       // have the same number of columns as the header row.
       if (rowIdx == range.end.row && footerRange) {
-        continue;
+        return;
       }
 
       if (row.length < expectedColumnCount) {
@@ -777,7 +751,7 @@ exports.SessionPerformMappingJob = (sid, range, mapping, includeErrorRow = false
     } else {
       warnings.push({ row: rowIdx, type: errorTypes.ValidationError.EmptyRow({}) })
     }
-  }
+  });
 
   let jid = makeAccessToken("j");
   let job = new JobResult(records, errors, warnings);
diff --git a/lib/importer/src/dudk/backend.test.js b/lib/importer/src/dudk/backend.test.js
index 6d471fc3..f3fcfff2 100644
--- a/lib/importer/src/dudk/backend.test.js
+++ b/lib/importer/src/dudk/backend.test.js
@@ -1,5 +1,6 @@
 const backend = require('./backend');
 const attributeTypes = require('./types/attribute-types');
+const Range = require('./util/range');
 
 const testFiles = new Map([
   ["test", [
@@ -53,11 +54,11 @@ describe("Backend tests", () => {
         ]),
       });
 
-      const dataRange = {
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 5, column: 2 }
-      };
+      const dataRange = new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 5, column: 2 }
+      );
 
       const samples = backend.SessionGetInputSampleRows(sid, dataRange,
         1, 1, 1);
@@ -133,11 +134,11 @@ describe("Backend tests", () => {
     const sid = backend.CreateSession();
     backend.SessionSetFile(sid, '../../fixtures/merged-cells.xlsx');
 
-    const dataRange = {
-      sheet: 'Cool Data',
-      start: { row: 3, column: 2 },
-      end: { row: 5, column: 5 }
-    };
+    const dataRange = new Range(
+      'Cool Data',
+      { row: 3, column: 2 },
+      { row: 5, column: 5 }
+    );
 
     const samples = backend.SessionGetInputSampleRows(sid, dataRange,
       1, 1, 1);
@@ -159,11 +160,11 @@ describe("Backend tests", () => {
       [{ index: 6, row: [{ value: 'Sid' }, undefined, { value: '10' }, { value: 'Medium' }] }]
     ]);
 
-    const allRange = {
-      sheet: 'Cool Data',
-      start: { row: 0, column: 0 },
-      end: { row: 7, column: 5 }
-    };
+    const allRange = new Range(
+      'Cool Data',
+      { row: 0, column: 0 },
+      { row: 7, column: 5 }
+    );
     const wholeSheet = backend.SessionGetInputSampleRows(sid,
       allRange,
       8, 0, 0);
@@ -301,11 +302,11 @@ describe("Backend tests", () => {
       const sid = backend.CreateSession();
       backend.SessionSetFile(sid, filename);
 
-      const dataRange = {
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 5, column: 3 }
-      };
+      const dataRange = new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 5, column: 3 }
+      );
 
       const samples = backend.SessionGetInputSampleRows(sid, dataRange,
         1, 1, 1);
@@ -329,38 +330,38 @@ describe("Backend tests", () => {
       const sid = backend.CreateSession();
       backend.SessionSetFile(sid, filename);
 
-      const headerRange = {
-        sheet: sheetname,
-        start: { row: 2, column: 0 },
-        end: { row: 2, column: 2 }
-      };
+      const headerRange = new Range(
+        sheetname,
+        { row: 2, column: 0 },
+        { row: 2, column: 2 }
+      );
 
-      const footerRange = {
-        sheet: sheetname,
-        start: { row: 6, column: 0 },
-        end: { row: 5, column: 1 }
-      };
+      const footerRange = new Range(
+        sheetname,
+        { row: 5, column: 0 },
+        { row: 6, column: 1 }
+      );
 
       const defaultDataRange = backend.SessionSuggestDataRange(sid, null, null);
-      expect(defaultDataRange).toMatchObject({
-        sheet: sheetname,
-        start: { row: 1, column: 0 },
-        end: { row: 6, column: 6 }
-      });
+      expect(defaultDataRange).toMatchObject(new Range(
+        sheetname,
+        { row: 1, column: 0 },
+        { row: 6, column: 6 }
+      ));
 
       const headerBasedDataRange = backend.SessionSuggestDataRange(sid, headerRange, null);
-      expect(headerBasedDataRange).toMatchObject({
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 6, column: 2 }
-      });
+      expect(headerBasedDataRange).toMatchObject(new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 6, column: 2 }
+      ));
 
       const headerAndFooterBasedDataRange = backend.SessionSuggestDataRange(sid, headerRange, footerRange);
-      expect(headerAndFooterBasedDataRange).toMatchObject({
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 6, column: 2 }
-      });
+      expect(headerAndFooterBasedDataRange).toMatchObject(new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 5, column: 2 }
+      ));
     }
   });
 
@@ -370,11 +371,11 @@ describe("Backend tests", () => {
       const sid = backend.CreateSession();
       backend.SessionSetFile(sid, filename);
 
-      const dataRange = {
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 5, column: 2 }
-      };
+      const dataRange = new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 5, column: 2 }
+      );
 
       // There are three rows available in the range. Let's see how the sampling
       // functions allocate them if we ask for too many sample rows.
@@ -451,11 +452,11 @@ describe("Backend tests", () => {
       const sid = backend.CreateSession();
       backend.SessionSetFile(sid, filename);
 
-      const dataRange = {
-        sheet: sheetname,
-        start: { row: 3, column: 0 },
-        end: { row: 5, column: 2 }
-      };
+      const dataRange = new Range(
+        sheetname,
+        { row: 3, column: 0 },
+        { row: 5, column: 2 }
+      );
 
       // We can be fairly confident startCount and endCount work right, but
       // middleCount has an *algorithm* that tries to pick a random sample of rows
@@ -536,11 +537,11 @@ test('validation', () => {
     const sid = backend.CreateSession();
     backend.SessionSetFile(sid, filename);
 
-    const dataRange = {
-      sheet: sheetname,
-      start: { row: 3, column: 0 },
-      end: { row: 8, column: 3 }
-    };
+    const dataRange = new Range(
+      sheetname,
+      { row: 3, column: 0 },
+      { row: 8, column: 3 }
+    );
 
     const mapping = {
       attributeMappings: {
@@ -600,11 +601,11 @@ test('validation', () => {
 test('guessing types', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/type-guessing.csv");
-  const dataRange = {
-    sheet: 'Sheet1',
-    start: { row: 1, column: 0 },
-    end: { row: 6, column: 9 }
-  };
+  const dataRange = new Range(
+    'Sheet1',
+    { row: 1, column: 0 },
+    { row: 6, column: 9 }
+  );
 
   const guesses = backend.SessionGuessTypes(sid, dataRange);
   expect(guesses).toMatchObject([
diff --git a/lib/importer/src/dudk/sheets.js b/lib/importer/src/dudk/sheets.js
index c2ab0652..2acc2c76 100644
--- a/lib/importer/src/dudk/sheets.js
+++ b/lib/importer/src/dudk/sheets.js
@@ -1,6 +1,7 @@
 const b26 = require('./util/base26')
 const backend = require("./backend");
 const attributeTypes = require('./types/attribute-types');
+const Range = require('./util/range');
 
 const DEFAULT_PREVIEW_LIMIT = 20
 
@@ -30,7 +31,7 @@ exports.GetHeader = (sid, sheet) => {
   } else {
     // We have a valid header range selected by a user, get the real
     // values from the sheet
-    const headerSample = backend.SessionGetInputSampleRows(sid, headerRange, 1, 0, 0);
+  const headerSample = backend.SessionGetInputSampleRows(sid, headerRange, 1, 0, 0);
     const samples = headerSample[0][0].row;
 
     for (let i = 0; i < samples.length; i++) {
@@ -127,11 +128,12 @@ exports.GetPreview = (sid, sheet, count = 10) => {
     .SessionGetInputDimensions(sid)
     .sheetDimensions.get(sheet);
 
-  const preview = backend.SessionGetInputSampleRows(sid, {
-    sheet: sheet,
-    start: { row: 0, column: 0 },
-    end: { row: dimensions.rows, column: dimensions.columns > 0 ? dimensions.columns - 1 : 0 }
-  }, Math.min(count, dimensions.rows), 0, 0)[0];
+  const previewRange = new Range(
+    sheet,
+    { row: 0, column: 0 },
+    { row: dimensions.rows, column: dimensions.columns > 0 ? dimensions.columns - 1 : 0 }
+  );
+  const preview = backend.SessionGetInputSampleRows(sid, previewRange, Math.min(count, dimensions.rows), 0, 0)[0];
 
   // TODO: Is there a better way to tell if the sheet is empty than iterating
   // all the cells? - we should have something in SessionGetInputDimensions
@@ -177,11 +179,11 @@ exports.GetRows = (sid, sheet, start = 0, count = 10) => {
 
   // Try to provide rows from start to start+count-1, but limit ourselves to
   // the rows in the sheet.
-  const rowRange = {
-    sheet: sheet,
-    start: { row: start, column: 0 },
-    end: { row: Math.min(start + count, sheetDimensions.rows), column: sheetDimensions.columns - 1 }
-  }
+  const rowRange = new Range(
+    sheet,
+    { row: start, column: 0 },
+    { row: Math.min(start + count, sheetDimensions.rows), column: sheetDimensions.columns - 1 }
+  );
   const wantedRows = rowRange.end.row - start;
   const preview = backend.SessionGetInputSampleRows(sid, rowRange, wantedRows, 0, 0)[0];
 
@@ -197,11 +199,11 @@ exports.GetRowRangeFromEnd = (sid, sheet, count = 10) => {
   const hRange = backend.SessionGetHeaderRange(sid, sheet)
 
   const end = sheetDimensions.rows - 1;
-  return {
-    sheet: sheet,
-    start: { row: Math.max(end - count, hRange.start.row + 1), column: hRange.start.column },
-    end: { row: end, column: hRange.end.column }
-  }
+  return new Range(
+    sheet,
+    { row: Math.max(end - count, hRange.start.row + 1), column: hRange.start.column },
+    { row: end, column: hRange.end.column }
+  );
 }
 
 // Given a session id and a sheet returns up to count rows.
@@ -220,22 +222,17 @@ exports.GetColumnValues = (sid, sheet, columnIndex, cellWidth = 30, count = 10)
   const fRange = backend.SessionGetFooterRange(sid, sheet)
 
   let dataRange = backend.SessionSuggestDataRange(sid, hRange, fRange);
-  // Limit to just the column we want
-  dataRange.start.column += columnIndex;
-  dataRange.end.column = dataRange.start.column;
-
-  // The range passed to SessionGetInputValues is inclusive, and therefore
-  // we end up with the first row of the selected footer. To avoid this
-  // we will decrement the end.row to ensure we don't pull too many values.
-  // We also need to make sure in small tables thast this doesn't make end.row
-  // less than start.row
-  if (dataRange.end.row > dataRange.start.row) {
-    dataRange.end.row = dataRange.end.row - 1
-  }
-
+  // Create a new Range for just the column we want
+  const colStart = dataRange.start.row;
+  const colEnd = dataRange.end.row > dataRange.start.row ? dataRange.end.row - 1 : dataRange.end.row;
+  const singleColRange = new Range(
+    dataRange.sheet,
+    { row: colStart, column: dataRange.start.column + columnIndex },
+    { row: colEnd, column: dataRange.start.column + columnIndex }
+  );
   let values = backend.SessionGetInputValues(
     sid,
-    dataRange,
+    singleColRange,
     count
   )[0];
 
diff --git a/lib/importer/src/dudk/sheets.test.js b/lib/importer/src/dudk/sheets.test.js
index bdbfc641..f7399dc2 100644
--- a/lib/importer/src/dudk/sheets.test.js
+++ b/lib/importer/src/dudk/sheets.test.js
@@ -10,11 +10,12 @@ test('trailing columns', () => {
     expect(sid).not.toBeNull();
 
     backend.SessionSetFile(sid, "../../fixtures/trailing-column.csv")
-    backend.SessionSetHeaderRange(sid, {
-        sheet: "Sheet1",
-        start: { row: 0, column: 0 },
-        end: { row: 0, column: 2 },
-    })
+    const Range = require('./util/range');
+    backend.SessionSetHeaderRange(sid, new Range(
+        "Sheet1",
+        { row: 0, column: 0 },
+        { row: 0, column: 2 }
+    ))
 
     let headers = sheets_lib.GetHeader(sid, "Sheet1")
     expect(headers.length).toBe(3);
diff --git a/lib/importer/src/dudk/types/date.test.js b/lib/importer/src/dudk/types/date.test.js
index e0745ec2..5802f8d1 100644
--- a/lib/importer/src/dudk/types/date.test.js
+++ b/lib/importer/src/dudk/types/date.test.js
@@ -1,5 +1,5 @@
 const date = require('./date'); // For unit tests
-const errors = require('../util/errors');
+const Range = require('../util/range');
 
 test('string date parsing', () => {
   const ymd = date.makeCombinedDateType(['year', 'month', 'day']);
@@ -100,11 +100,11 @@ const at = require('./attribute-types');
 test('dates in ods', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/dates.ods");
-  const dataRange = {
-    sheet: 'Sheet1',
-    start: { row: 0, column: 0 },
-    end: { row: 3, column: 0 }
-  };
+  const dataRange = new Range(
+     'Sheet1',
+     { row: 0, column: 0 },
+     { row: 3, column: 0 }
+  );
   const mapping = {
     attributeMappings: {
       Date: 0
@@ -147,11 +147,11 @@ test('dates in ods', () => {
 test('dates in csv', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/dates.csv");
-  const dataRange = {
-    sheet: 'Sheet1',
-    start: { row: 2, column: 1 },
-    end: { row: 8, column: 1 }
-  };
+  const dataRange = new Range(
+    'Sheet1',
+    { row: 2, column: 1 },
+    { row: 8, column: 1 }
+  );
   const mapping = {
     attributeMappings: {
       Date: 0
@@ -200,11 +200,11 @@ test('dates in csv', () => {
 test('dates in xlsx from numbers', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/dates.numbers.xlsx");
-  const dataRange = {
-    sheet: 'Sheet 1',
-    start: { row: 2, column: 1 },
-    end: { row: 8, column: 1 }
-  };
+  const dataRange = new Range(
+    'Sheet 1',
+    { row: 2, column: 1 },
+    { row: 8, column: 1 }
+  );
   const mapping = {
     attributeMappings: {
       Date: 0
@@ -247,11 +247,11 @@ test('dates in xlsx from numbers', () => {
 test('dates in xlsx from office 2016', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/dates.office2016.xlsx");
-  const dataRange = {
-    sheet: 'Sheet1',
-    start: { row: 2, column: 1 },
-    end: { row: 3, column: 1 }
-  };
+  const dataRange = new Range(
+    'Sheet1',
+    { row: 2, column: 1 },
+    { row: 3, column: 1 }
+  );
   const mapping = {
     attributeMappings: {
       Date: 0
@@ -289,11 +289,11 @@ test('dates in xlsx from office 2016', () => {
 test('dates in xls from office 2016', () => {
   const sid = backend.CreateSession();
   backend.SessionSetFile(sid, "../../fixtures/dates.office2016.xls");
-  const dataRange = {
-    sheet: 'Sheet1',
-    start: { row: 2, column: 1 },
-    end: { row: 3, column: 1 }
-  };
+  const dataRange = new Range(
+   'Sheet1',
+   { row: 2, column: 1 },
+   { row: 3, column: 1 }
+  );
   const mapping = {
     attributeMappings: {
       Date: 0
diff --git a/lib/importer/src/dudk/util/range.js b/lib/importer/src/dudk/util/range.js
new file mode 100644
index 00000000..e7a3a3d1
--- /dev/null
+++ b/lib/importer/src/dudk/util/range.js
@@ -0,0 +1,104 @@
+class Range {
+    constructor(sheet, start, end) {
+        // start and end: { row: Number, column: Number }
+        if (!sheet || !start || !end) {
+            throw new Error('Range requires sheet, start, and end');
+        }
+        this.sheet = sheet;
+        this.start = {
+            row: Math.min(start.row, end.row),
+            column: Math.min(start.column, end.column)
+        };
+        this.end = {
+            row: Math.max(start.row, end.row),
+            column: Math.max(start.column, end.column)
+        };
+    }
+
+    // Returns true if the range is valid (end >= start for both row and column)
+    isValid() {
+        return this.end.row >= this.start.row && this.end.column >= this.start.column;
+    }
+
+    // Apply a function to each row index in the range
+    // inclusive=true: includes end row (default, spreadsheet style)
+    // inclusive=false: excludes end row (half-open interval)
+    applyRows(fn, inclusive = true) {
+        const end = inclusive ? this.end.row : this.end.row - 1;
+        for (let r = this.start.row; r <= end; r++) {
+            fn(r);
+        }
+    }
+
+
+    // Inclusive row indices
+    *rows(inclusive = true) {
+        const end = inclusive ? this.end.row : this.end.row - 1;
+        for (let r = this.start.row; r <= end; r++) {
+            yield r;
+        }
+    }
+
+    // Inclusive column indices
+    *columns(inclusive = true) {
+        const end = inclusive ? this.end.column : this.end.column - 1;
+        for (let c = this.start.column; c <= end; c++) {
+            yield c;
+        }
+    }
+
+    // Iterate over all cells (row, col) in the range
+    *cells(inclusive = true) {
+        const endRow = inclusive ? this.end.row : this.end.row - 1;
+        const endCol = inclusive ? this.end.column : this.end.column - 1;
+        for (let r = this.start.row; r <= endRow; r++) {
+            for (let c = this.start.column; c <= endCol; c++) {
+                yield { row: r, column: c };
+            }
+        }
+    }
+
+    // Number of rows in the range
+    numRows(inclusive = true) {
+        return (this.end.row - this.start.row) + (inclusive ? 1 : 0);
+    }
+
+    // Number of columns in the range
+    numCols(inclusive = true) {
+        return (this.end.column - this.start.column) + (inclusive ? 1 : 0);
+    }
+
+    // Area (number of cells) in the range
+    area(inclusive = true) {
+        return this.numRows(inclusive) * this.numCols(inclusive);
+    }
+
+    // Convert column index to Base26 (A, B, ..., Z, AA, AB, ...)
+    static colToBase26(column) {
+        // Use the base26 utility, which expects 1-based input
+        const base26 = require('./base26');
+        return base26.toBase26(column + 1);
+    }
+
+    // Convert row index to 1-based (spreadsheet style)
+    static rowTo1Based(row) {
+        return (row + 1).toString();
+    }
+
+    // Get Base26 notation for start cell (e.g., "A1")
+    get startBase26() {
+        return `${Range.colToBase26(this.start.column)}${Range.rowTo1Based(this.start.row)}`;
+    }
+
+    // Get Base26 notation for end cell (e.g., "C10")
+    get endBase26() {
+        return `${Range.colToBase26(this.end.column)}${Range.rowTo1Based(this.end.row)}`;
+    }
+
+    // Get A1-style range string (e.g., "Sheet1!A1:C10")
+    toA1String() {
+        return `${this.sheet}!${this.startBase26}:${this.endBase26}`;
+    }
+}
+
+module.exports = Range;
diff --git a/lib/importer/src/dudk/util/range.test.js b/lib/importer/src/dudk/util/range.test.js
new file mode 100644
index 00000000..bda8bcd1
--- /dev/null
+++ b/lib/importer/src/dudk/util/range.test.js
@@ -0,0 +1,93 @@
+const Range = require('./range');
+
+describe('Range', () => {
+  test('applyRows applies function to each row (inclusive)', () => {
+    const r = new Range('Sheet1', { row: 2, column: 0 }, { row: 4, column: 1 });
+    const rows = [];
+    r.applyRows((rowIdx) => rows.push(rowIdx));
+    expect(rows).toEqual([2, 3, 4]);
+  });
+
+  test('applyRows applies function to each row (exclusive)', () => {
+    const r = new Range('Sheet1', { row: 2, column: 0 }, { row: 4, column: 1 });
+    const rows = [];
+    r.applyRows((rowIdx) => rows.push(rowIdx), false);
+    expect(rows).toEqual([2, 3]);
+  });
+
+  const sheet = 'Sheet1';
+  const start = { row: 1, column: 2 }; // C2
+  const end = { row: 3, column: 4 };   // E4
+
+  test('constructs and normalizes start/end', () => {
+    const r = new Range(sheet, end, start); // reversed
+    expect(r.sheet).toBe(sheet);
+    expect(r.start).toEqual({ row: 1, column: 2 });
+    expect(r.end).toEqual({ row: 3, column: 4 });
+  });
+
+  test('rows() yields correct indices (inclusive/exclusive)', () => {
+    const r = new Range(sheet, start, end);
+    expect([...r.rows()]).toEqual([1, 2, 3]);
+    expect([...r.rows(false)]).toEqual([1, 2]);
+  });
+
+  test('columns() yields correct indices (inclusive/exclusive)', () => {
+    const r = new Range(sheet, start, end);
+    expect([...r.columns()]).toEqual([2, 3, 4]);
+    expect([...r.columns(false)]).toEqual([2, 3]);
+  });
+
+  test('cells() yields all cell coordinates (inclusive/exclusive)', () => {
+    const r = new Range(sheet, start, end);
+    const allCells = [...r.cells()];
+    expect(allCells.length).toBe(9); // 3 rows x 3 cols
+    expect(allCells[0]).toEqual({ row: 1, column: 2 });
+    expect(allCells[8]).toEqual({ row: 3, column: 4 });
+    const exclCells = [...r.cells(false)];
+    expect(exclCells.length).toBe(4); // 2 rows x 2 cols
+    expect(exclCells[0]).toEqual({ row: 1, column: 2 });
+    expect(exclCells[3]).toEqual({ row: 2, column: 3 });
+  });
+
+  test('numRows, numCols, area (inclusive/exclusive)', () => {
+    const r = new Range(sheet, start, end);
+    expect(r.numRows()).toBe(3);
+    expect(r.numRows(false)).toBe(2);
+    expect(r.numCols()).toBe(3);
+    expect(r.numCols(false)).toBe(2);
+    expect(r.area()).toBe(9);
+    expect(r.area(false)).toBe(4);
+  });
+
+  test('colToBase26 converts indices to spreadsheet letters', () => {
+    expect(Range.colToBase26(0)).toBe('A');
+    expect(Range.colToBase26(25)).toBe('Z');
+    expect(Range.colToBase26(26)).toBe('AA');
+    expect(Range.colToBase26(27)).toBe('AB');
+    expect(Range.colToBase26(51)).toBe('AZ');
+    expect(Range.colToBase26(52)).toBe('BA');
+  });
+
+  test('rowTo1Based converts indices to 1-based strings', () => {
+    expect(Range.rowTo1Based(0)).toBe('1');
+    expect(Range.rowTo1Based(9)).toBe('10');
+  });
+
+  test('startBase26 and endBase26 getters', () => {
+    const r = new Range(sheet, start, end);
+    expect(r.startBase26).toBe('C2');
+    expect(r.endBase26).toBe('E4');
+  });
+
+  test('toA1String returns correct A1 notation', () => {
+    const r = new Range(sheet, start, end);
+    expect(r.toA1String()).toBe('Sheet1!C2:E4');
+  });
+
+  test('throws if missing arguments', () => {
+    expect(() => new Range()).toThrow();
+    expect(() => new Range(sheet)).toThrow();
+    expect(() => new Range(sheet, start)).toThrow();
+  });
+});
diff --git a/lib/importer/src/dudk/validation.test.js b/lib/importer/src/dudk/validation.test.js
index e4c4118f..3fa3e24e 100644
--- a/lib/importer/src/dudk/validation.test.js
+++ b/lib/importer/src/dudk/validation.test.js
@@ -6,6 +6,7 @@ const session = require('../session');
 const backend = require('./backend');
 const attributeTypes = require('./types/attribute-types');
 const mock_files = require('mock-fs');
+const Range = require('./util/range');
 
 function localFileMock(file, data) {
     const obj = {}
@@ -47,11 +48,11 @@ describe("Validation tests", () => {
             localFileMock('./empty/app/config.json', JSON.stringify(config))
             process.env.KIT_PROJECT_DIR = './empty/app/config.json'
 
-            const dataRange = {
-                sheet: "Sheet1",
-                start: { row: 0, column: 0 },
-                end: { row: 2, column: 10 }
-            };
+            const dataRange = new Range(
+                "Sheet1",
+                { row: 0, column: 0 },
+                { row: 2, column: 10 }
+            );
 
             const mapping = createTestMapping(
                 {
@@ -110,11 +111,11 @@ describe("Validation tests", () => {
             localFileMock('./empty/app/config.json', JSON.stringify(config))
             process.env.KIT_PROJECT_DIR = './empty/app/config.json'
 
-            const dataRange = {
-                sheet: "Sheet1",
-                start: { row: 0, column: 0 },
-                end: { row: 2, column: 10 }
-            };
+            const dataRange = new Range(
+                "Sheet1",
+                { row: 0, column: 0 },
+                { row: 2, column: 10 }
+            );
 
             const mapping = createTestMapping(
                 {
@@ -174,11 +175,11 @@ describe("Validation tests", () => {
             localFileMock('./empty/app/config.json', JSON.stringify(config))
             process.env.KIT_PROJECT_DIR = './empty/app/config.json'
 
-            const dataRange = {
-                sheet: "Sheet1",
-                start: { row: 0, column: 0 },
-                end: { row: 2, column: 10 }
-            };
+            const dataRange = new Range(
+                "Sheet1",
+                { row: 0, column: 0 },
+                { row: 2, column: 10 }
+            );
 
             const mapping = createTestMapping(
                 {
@@ -236,11 +237,11 @@ describe("Validation tests", () => {
             localFileMock('./empty/app/config.json', JSON.stringify(config))
             process.env.KIT_PROJECT_DIR = './empty/app/config.json'
 
-            const dataRange = {
-                sheet: "Sheet1",
-                start: { row: 0, column: 0 },
-                end: { row: 2, column: 10 }
-            };
+            const dataRange = new Range(
+                "Sheet1",
+                { row: 0, column: 0 },
+                { row: 2, column: 10 }
+            );
 
             const mapping = createTestMapping(
                 {
diff --git a/lib/importer/src/index.js b/lib/importer/src/index.js
index 26ee7c2d..839d975d 100644
--- a/lib/importer/src/index.js
+++ b/lib/importer/src/index.js
@@ -7,6 +7,7 @@ const sheets_lib = require("./dudk/sheets.js");
 const tpl_functions = require("./functions.js")
 const tpl_filters = require("./filters.js")
 const usage = require("./usage.js")
+const Range = require("./dudk/util/range.js");
 
 const IMPORTER_SESSION_KEY = "importer.session";
 const IMPORTER_ERROR_KEY = "importer.error";
@@ -216,11 +217,11 @@ exports.Initialise = (config, router, prototypeKit) => {
       // should default to the first row in the sheet.
       let maxCol = sheets_lib.GetTotalColumns(session.backendSid, session.sheet);
 
-      session.headerRange = {
-        sheet: session.sheet,
-        start: { row: -1, column: 0 },
-        end: { row: -1, column: maxCol - 1 },
-      };
+      session.headerRange = new Range(
+        session.sheet,
+        { row: -1, column: 0 },
+        { row: -1, column: maxCol - 1 },
+      );
 
       // Ensure the session is persisted. Currently in session, eventually another way
       request.session.data[IMPORTER_SESSION_KEY] = session;
@@ -250,11 +251,11 @@ exports.Initialise = (config, router, prototypeKit) => {
       // If the user did not select a header range, then we should create one
       if (session.headerRange == null) {
         let [minCol, maxCol] = sheets_lib.GuessHeaderRange(session.backendSid, session.sheet);
-        session.headerRange = {
-          sheet: session.sheet,
-          start: { row: -1, column: minCol },
-          end: { row: -1, column: maxCol },
-        };
+        session.headerRange = new Range(
+          session.sheet,
+          { row: -1, column: minCol },
+          { row: -1, column: maxCol },
+        );
       }
 
       // Ensure the session is persisted. Currently in session, eventually another way
@@ -606,9 +607,9 @@ const getSelectionFromRequest = (request, session, optional = false) => {
     [tlCol, brCol] = [brCol, tlCol];
   }
 
-  return {
-    sheet: session.sheet,
-    start: { row: tlRow, column: tlCol },
-    end: { row: brRow, column: brCol },
-  };
+  return new Range(
+    session.sheet,
+    { row: tlRow, column: tlCol },
+    { row: brRow, column: brCol },
+  );
 };
diff --git a/lib/importer/src/session.js b/lib/importer/src/session.js
index 1f2a8254..d2c8bc5d 100644
--- a/lib/importer/src/session.js
+++ b/lib/importer/src/session.js
@@ -29,11 +29,10 @@ class Session {
   set headerRange(range) {
     if (!range) return;
 
-    const r = range;
-    if (!r.sheet) {
-      r.sheet = this.sheet
+    if (!range.sheet) {
+      range.sheet = this.sheet
     }
-    backend.SessionSetHeaderRange(this.backendSid, r)
+    backend.SessionSetHeaderRange(this.backendSid, range)
   }
 
   get footerRange() {
@@ -41,12 +40,11 @@ class Session {
   }
 
   set footerRange(range) {
-    const r = range;
-    if (!r.sheet) {
-      r.sheet = this.sheet
+    if (!range.sheet) {
+      range.sheet = this.sheet
     }
 
-    backend.SessionSetFooterRange(this.backendSid, r)
+    backend.SessionSetFooterRange(this.backendSid, range)
   }
 
   get mapping() {
diff --git a/lib/importer/src/session.test.js b/lib/importer/src/session.test.js
index 25ac4ba2..657e219b 100644
--- a/lib/importer/src/session.test.js
+++ b/lib/importer/src/session.test.js
@@ -1,4 +1,5 @@
 const session_lib = require('./session');
+const Range = require('./dudk/util/range');
 
 const basic_config = {
     fields: [{ name: 'field', type: 'text', required: false }],
@@ -42,7 +43,7 @@ describe("Header Row Display tests", () => {
 
 
         s.sheet = "Sheet1"
-        s.headerRange = { sheet: "Sheet1", start: { row: 0, column: 0 }, end: { row: 0, column: 2 } }
+        s.headerRange = new Range("Sheet1", { row: 0, column: 0 }, { row: 0, column: 2 } );
         const headers = session_lib.HeaderRowDisplay(s, "None")
         expect(headers).toBeNull();
     });
@@ -81,7 +82,7 @@ describe("Header Row Display tests", () => {
         ).session;
 
         s.sheet = "Sheet1"
-        s.headerRange = { sheet: "Sheet1", start: { row: 0, column: 0 }, end: { row: 0, column: 2 } }
+        s.headerRange = new Range("Sheet1", { row: 0, column: 0 }, { row: 0, column: 2 });
 
         const headers = session_lib.HeaderRowDisplay(s, "index")
         expect(headers).toStrictEqual(["A", "B", "C"])
@@ -140,9 +141,11 @@ describe("Header Row Display tests", () => {
         ).session;
 
         s.sheet = "Sheet1"
-        s.headerRange = {
-            sheet: "Sheet1", start: { row: 0, column: 1 }, end: { row: 1, column: 3 }
-        }
+        s.headerRange = new Range(
+            'Sheet1',
+            { row: 0, column: 1 },
+            { row: 1, column: 3 }
+        );
 
         const headers = session_lib.HeaderRowDisplay(s, "source")
         expect(headers).toStrictEqual(["Title", "First name", "Surname"]);