Reading the spec from the top, the Introduction and then Goals section are very high-level, and the abrupt transition to fine-grained details in the next section (Use Cases) is jarring.
I suggest some bridging content that links the two sections - something that explains what I am about to read and why it is relevant to the high level content that I just read.
Specifically, because the document has four distinct topics (data model, validation, rendering and selective obfuscation), it would be great to explain that at a high level to prepare a structure in the reader's mind to hold the information that they are about to read.