I realize that we are getting into some finer semantics, but given that the purpose of this discussion is a common definition of terms, it would seem reasonable to do so.
Deborah – you seem to be mixing the abilities of the file format with the specific implementation choices of an author using that format. The format is portable, because it allows the content to be used in all of those environments in a common manner. The fact that a given author of content for that format chose to do something strange (be it colors or offscreen or whatever) has NOTHING to do with the formats ability to be portable.
Leonard
From: Deborah Kaplan
Date: Friday, September 4, 2015 at 1:41 PM
To: Leonard Rosenthol
Cc: Ivan Herman, W3C Digital Publishing IG, Ralph Swick, Bill Kasdorf, Bill McCoy
Subject: Re: [Glossary] Definition of a portable document (and other things...)
A certain amount of adaptation is necessary before you can call something "portable." If you create a webpage which is cyan font on a cyan background on every browser except for Internet Explorer 6, does it matter that the format *allows* adaptability? I would argue that is not portable document. Similarly, if you created a website where every aspect of content was offscreen, and therefore only available to screen reader users, that would also quite arguably not be portable, by any useful definition. In both of these cases the formats allow for adaptability, but in neither of these cases are the documents themselves actually useful if they are in any way ported.
Given this constraint, "portability," actually has some rather wonderful implications for accessibility. If a website with all the text only available to screen reader users (a straw man example) isn't portable, then it is equally true that a website where all the text is images without alt (not a straw man at all, as examples exist all over the web) is not portable.
Adaptability doesn't have to mean a complicated website looks great in ibooks; it means the essential components of the document are available when the document's context is changed. (The "graceful degradation" aspect Ivan and Leonard are discussing upthread.
Deborah