"is valid" algorithm uses a concept of "size of" that is not defined

[bzbarsky]

Things like:

If sr’s startOffset is greater than the size of the startContainer,

Presumably it means "the number of children of the startContainer". That's the terminology other specs use for this.

[bzbarsky]

Actually, no, that's not right for textnodes.

What you probably want is https://dom.spec.whatwg.org/#concept-node-length complete with a link to it.

[garykac]

This issue was moved to w3c/staticrange#5