The manual entry for REQUEST DOCUMENT says:

[ENCODED [[FOR TYPE[S]operand14…] [IN] CODEPAGEoperand15]]
operand14 is the list of mime-types for which an encoding of the returned document in operand13 will be performed.

So that seems to say that you can provide more than one MIME type. But operand14 can’t be an array, it doesn’t say how you would delimit the items in the list, and none of the delimiters I’ve tried (space, comma, semicolon, colon) is working. Has anyone else figured out a way to specify more than one type?

Thanks to a tip from Steve Robinson on the SAG-L list, I now know the answer. I should have paid more attention to the ellipsis after operand14. The correct way is to code multiple instances of operand14, for example:

REQUEST DOCUMENT FROM 'http://www.example.com/  '
   PAGE #PAGE ENCODED FOR TYPES 'text/xml' 'text/html' CODEPAGE 'utf-8'