body rule only for txt or html?

[Tobi]

Hello list

ifplugin Mail::SpamAssassin::Plugin::ExtractText
    extracttext_external  pdfgrep  /usr/bin/pdfgrep .+ {}
    extracttext_use       pdfgrep  .pdf application/pdf
endif

which leads to the fact that body rules then can also hit on pdf
content. Is there a possibility for a rule to search only in the text
and/or html representation of a message?

Cheers

tobi