The result of the search - the man page source files on the system - can be passed back to man in local mode to read each page.
man -wK --regex 'Brace Expansion' | sort -u | xargs man -l -P cat | grep -inF 'Brace Expansion'
The regex used for the man command search is case-insensitive by default. The list of results from the search is sorted and any duplicates are removed. Then, it is passed back to man using
xargs. By using the
cat pager, each processed man page can be printed to the standard output. At that point, the data is a stream of plain text on which grep can operate.
-l option of
man is used to activate local mode, where it parses a file directly instead of parsing the system's MANPATH.
-P cat option of
man sets the pager to
cat. This means the processed man page will be displayed using
-i option of
grep is used for case-insensitive search. The
-n option prints out line numbers (simply added for convenience). The
-F option specifies that the pattern is a fixed string.