font measure "Courier -12" "-display"
should return the width of the string "-display" in
pixels. Instead, it raises an error, because the string
"-display" is interpreted as the abbreviation of the
optional "-displayof" switch. This is a very
long-standing bug in parsing the "font measure"
command, whose syntax is
font measure font ?-displayof window? text
If the "font" argument is followed by a single string
then the correct behavior should be to interpret that
string as the "text" argument, regardless of what
string was passed to the command.