Does XML Spec define that it is illegal to have whitespace before self closing slash?

Question

I am talking XML document not HTML. Since in HTML,
and
are both valid. Want to know if XML specification defines whether it is

Answer 1

The space at the end is allowed for "normal" tags as well as for empty elements, see https://www.w3.org/TR/xml/#sec-starttags:

Start-tag

STag ::= '<' Name (S Attribute)* S? '>'

Tags for Empty Elements

EmptyElemTag ::= '<' Name (S Attribute)* S? '/>'

Notice the S? at the end which optionally allows one or more whitespace characters at the end:

S ::= (#x20 | #x9 | #xD | #xA)+