Are single quotes valid in HTML/XHTML?

Question

Are single quotes valid in HTML? And more specifically: XHTML strict.

<table width="100%">
<table width='100%'>

Answer 1

Yes, single quotes are valid.

From the XML spec:

[10]   AttValue  ::= '"' ([^<&"] | Reference)* '"'
                  |  "'" ([^<&'] | Reference)* "'"