We treat @content-type and friends different in standard specs

[xml-project]

For most step we say that it is an error if option content-type or override-content-type is not a valid media type of the form “type/subtype+ext” or “type/subtype”. This is true for:

p:http-request/@headers?content-type
p:archive-manifest raises XD0079 if entry in override-content-types is not valid.
p:cast-content-type
p:text-join
p:uncompress

but not for

p:load (and therefor not for p:document and p:os-exec)
p:http-request/@parameters?override-content-type
p:css-formatter
p:xsl-formatter

I suggest that it is always an error.

[xml-project]

Fixed with pr #417