The error conditions under 5.6.3 fn:replace which raise err:FORX0004 should only be raised if the q flag has not been set, so it would be useful to add this condition to the descriptions. Currently these state:

A dynamic error is raised [err:FORX0004] if the value of $replacement contains a "$" character that is not immediately followed by a digit 0-9 and not immediately preceded by a "\".

A dynamic error is raised [err:FORX0004] if the value of $replacement contains a "\" character that is not part of a "\\" pair, unless it is immediately followed by a "$" character.


See the example under the section about the q flag in 5.6.1.1 Flags (which expects some output not an error): 
fn:replace("a/b/c", "/", "$", "q") returns "a$b$c"

[I will add this example (and others) as test cases to the QT3 fn-replace test set in anticipation of this clarification; see fn-replace-49 to 53.]