A rare syntax highlighting problem results from an extremely unfortunate
notation for octal numbers in IDL: "123. This unpaired quotation
mark is very difficult to parse, given that it can be mixed on a single
line with any number of strings. Emacs will incorrectly identify this
as a string, and the highlighting of following lines of code can be
distorted, since the string is never terminated.
One solution to this involves terminating the mistakenly identified string yourself by providing a closing quotation mark in a comment:
string("305B) + $ ;" <--- for font-lock
' is an Angstrom.'
A far better solution is to abandon this notation for octals altogether, and use the more sensible alternative IDL provides:
string('305'OB) + ' is an Angstrom.'
This simultaneously solves the font-lock problem and is more
consistent with the notation for hexadecimal numbers, e.g., 'C5'XB.