Highlighting after a line limit

Question

I'd like to highlight sections of a document which are too long (measured in lines) so they will all print on a physical page. Sections are separated with ===. I tried to do it with this code:

matchadd('ErrorMsg', '\%(^\|===\n\)\%(.*\n\)\{5}\zs\%(.*\n\)\+\ze', -1)

Everything works hunky-dory. But when I increase the size:

matchadd('ErrorMsg', '\%(^\|===\n\)\%(.*\n\)\{80}\zs\%(.*\n\)\+\ze', -1)

matches don't highlight. From the documentation :matchadd:

Defines a pattern to be highlighted in the current window (a
    "match")

Based on figuring out where exactly the problem happens, I think it's not using text outside the current window. What should I be doing instead? Sections are already associated with folds if that helps.

Answer 1

How about :au BufWinEnter * let w:m1=matchadd('ErrorMsg', '\(^===\)\_p\{20,}\1', -1) ?

This works with my little lorem ipsum test case.

The solution here is \_p\{20,}, which matches at least 20 printable characters including newline (that is the _).

I tried this with a little "lorem ipsum", consecutive blocks are also highlighted, which makes the whole affair quite colorful...