Thursday, April 30, 2009

XML Comments in XMP

Nowhere in the XMP or RDF specifications is any mention of XML comments.

On validating our vast set of PDF files gathered from the wild, thanks to sites like, and we have run into a multitude of cases where XMP produced by reputable (read "Adobe") products includes XML comments.

After consulting with collegues at Adobe, Solid Documents and PDFlib we reached consesus on this topic. 

Two conclusions:
  1. Since XML comments are legal XML and not explicitly prohibited, we conclude that they are allowed.
  2. XML comments may be dropped when converting PDF files based on this clause from the XML specification:
"an XML processor MAY, but need not, make it possible for an application to retrieve the text of comments"

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