Including plain text: CDATA

I followed Bob Stayton's advice in "Chapter 19. Modular DocBook files;
Including plain text" of his "DocBook XSL: The Complete Guide".

Is there any good solution if the included file contains the "special"
XML characters (&, <, >, and ")? I don't want these characters to be
converted to their respective entities, but instead want to wrap them
in CDATA sections to appear verbatim in the output.

Michael
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