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Showing Lines That Match Regular Expressions
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   To show in which sections differences occur for files that are not
source code for C or similar languages, use the `-F REGEXP' or
`--show-function-line=REGEXP' option.  `diff' considers lines that
match the argument REGEXP to be the beginning of a section of the file.
Here are suggested regular expressions for some common languages:

`^[A-Za-z_]'
     C, C++, Prolog

`^('
     Lisp

`^@\(chapter\|appendix\|unnumbered\|chapheading\)'
     Texinfo

   This option does not automatically select an output format; in order
to use it, you must select the context format (Note: Context Format)
or unified format (Note: Unified Format).  In other output formats it
has no effect.

   The `-F' and `--show-function-line' options find the nearest
unchanged line that precedes each hunk of differences and matches the
given regular expression.  Then they add that line to the end of the
line of asterisks in the context format, or to the `@@' line in unified
format.  If no matching line exists, they leave the output for that
hunk unchanged.  If that line is more than 40 characters long, they
output only the first 40 characters.  You can specify more than one
regular expression for such lines; `diff' tries to match each line
against each regular expression, starting with the last one given.  This
means that you can use `-p' and `-F' together, if you wish.