Documentation for BASIC "Is" keyword is missing, like in
> If A Is Nothing Then MsgBox "Foo"
E.g.. VBA has  for the topic. Generally, "Is" should behave similarly to our "EqualUnoObjects", but not limited to UNO objects. Anyway, even if it's limited to "Is Nothing" in LibreOffice BASIC, it needs a documentation.
Example reference pages for a new help page are:
The help page should consider x-referencing isObject() and EqualUnoObjects() Basic functions in order to clarify their differences.
Rafael Lima committed a patch related to this issue.
It has been pushed to "master":
tdf#143687 Document the "IS" Basic keyword