x1514 core—As TS (Katy) I want to register sections that have been split into two areas of the slide and named differently

[khelwood]

Allow a section number to be of the form [1-9][0-9]*[a-z]*
(a positive integer followed by zero or more letters).

e.g. section 8a and section 8b

Once release Katy to put patch for - 0068135 (DA39-END-0-FO-4-S8a & DA39-END-0-FO-4-S8b) & 0076907 (DA39-END-0-FO-4-S7a & DA39-END-0-FO-4-S7b)