texdoc bidi

[Karl Berry]

    containing "manual" and "doc" so that <package>-(manual|doc).pdf can win
    over <package>.pdf in general. 

Good! I think that would be highly desirable.

    I don't know in how many cases <package>.pdf is the most important
    document and <package>-(manual|doc).pdf are less important.

My guess is "never".  If the author has explicitly added a <known
suffix>, it seems to me it is 99% likely that it is the user manual.

In the past (before you were involved, Takuto), I recommended that
people use <pkg>-manual.pdf for the user manual, because that makes it
explicitly clear. <pkg>-doc.pdf is the same thing. --best, karl.