[Fontinst] accessing unencoded charecters

[Walter Schmidt]

Hi!

Assuming there is an mtx file for a re-encoded font, which 
says
      \setscalednotglyph{space}...

i.e., the space charecter is present in the real font, but
not in the re-encoded one.

Now I'm going to use this mtx file in an \installfont command.
How can I determine the width of the space charecter?  
Using the command 

      \width{space}

in the .etx file would result in an error:

  ! Missing number, treated as zero.
  <to be read again>
                     \g-space

Further question:  The command \ifsiglyph{space} would return 
"false" in this case.  How can I check for the existence of
a character, regardles of whether or not it is present in the
current encoding?

thank you in advance for any help
Walter