The description of the id() function, and of the new element-with-id() function, says that "Each xs:string in $arg is parsed as if it were of type IDREFS". If this were taken literally, an error condition would result if the string did not contain at least one token, since xs:IDREFS has a minLength of 1. The subsequent text of the paragraph makes it clear this is not the intent, but the phrase is nevertheless misleading. 

Proposal: change the sentence from

"Each xs:string in $arg is parsed as if it were of type IDREFS, that is, each xs:string in $arg is treated as a whitespace-separated sequence of tokens, each acting as an IDREF." 

to

"Each xs:string in $arg is treated as a whitespace-separated sequence of tokens, each acting as an IDREF."

Furthermore, later in the paragraph there is some confusing typography, where "IDREF" in small caps is followed by a lower-case "s" in normal font; it takes a keen eye to spot that this is the plural of IDREF rather than the word "IDREFS". I propose to change it to "IDREF values".