Dan Jacobson submitted the following bug to the Debian bug tracking
system :

something is wrong with masquerade, but I'm not sure what

$ checklink  --masquerade  $PWD  http://www.w3.org/TR/MathML2/ /dev/null
W3C checklink version 3.06 (c) 1999-2002 W3C
GET file:/tmp  fetched in 0.0s

Processing      file:/tmp/

Parsing...
 done (24 lines in 0.0s).
Checking anchors...
 done.
[Sun Apr  6 05:12:50 2003] checklink: Use of uninitialized value in
concatenation (.) or string at /usr/bin/checklink line 489.
processing file:/tmp/etmpja.txt.html in base 1
[Sun Apr  6 05:12:50 2003] checklink: Use of uninitialized value in
concatenation (.) or string at /usr/bin/checklink line 492.
[Sun Apr  6 05:12:50 2003] checklink: Use of uninitialized value in
concatenation (.) or string at /usr/bin/checklink line 489.
processing file:/tmp/reportbug-13348-0 in base 1
[Sun Apr  6 05:12:50 2003] checklink: Use of uninitialized value in
concatenation (.) or string at /usr/bin/checklink line 492.
[Sun Apr  6 05:12:50 2003] checklink: Use of uninitialized value in
concatenation (.) or string at /usr/bin/checklink line 489.

etc.