I think this post belongs to this category about the Octave Discourse site.
The issue is that the interpreter does not support line continuations in single-quoted strings. For example,
str = 'this is a string \ that runs on in the highlighter';
The entire string is highlighted, whereas it should end on a single line.
I don’t know where the syntax file for Discourse is located but it needs to be updated.
The same problem also exists with the Qscintilla syntax highlighter used in the GUI text editor. I have filed a bug report about that here: GNU Octave - Bugs: bug #59885, Qscintilla syntax file should not... [Savannah].