[XeTeX] missing characters and msgs

[Mike Maxwell]

I'm getting a msg from xetex about missing characters in a font; I'm 
unclear whether I should worry.  The output looks OK, I think, but I 
still worrry :-)

The warning is:
-----------
Missing character: There is no X in font 
[/groups/tools/fonts/NafeesNastaleeq
_v1_02.ttf]/ICU:script=arab,!
-----------
Some comments:
1) The actual missing character is not X, but U+200C = ZWNJ.
2) At the end of the xelatex run, I get the msg
       LaTeX Font Info:    Some font shapes were not available,
       defaults substituted.
    I'm guessing this means that xelatex substituted a ZWNJ from
    some other font, in which case maybe the original error msg
    could be improved to say that (like "There is no X in font
    uglification, using font glitzy for this character.")
3) Is there some way to turn off msgs I'm not interested in?
    For example, "Overfull \hbox (1.52164pt too wide)" is probably
    not something I'm worried about, whereas "Overfull \hbox
    (14.22636pt too wide)" probably is.  Likewise I don't think I
    need to see "Package changebar: In vtryfc, page 168,
    \cb at pagecount=367" or "\d at lta=\count148" (from the overpic
    package)--or if I do, I don't know why.  And I would like
    to turn off almost all warnings the first two passes through
    xelatex, reserving them for the third pass (errors that stop
    processing are, of course, a different thing).
-- 
    Mike Maxwell
    What good is a universe without somebody around to look at it?
    --Robert Dicke, Princeton physicist