[address1
][,
address2
]N
Append next input line to contents of pattern space; the two lines are separated by an embedded newline. (This command is designed to allow pattern matches across two lines.) Using \n to match the embedded newline, you can match patterns across multiple lines. See example under D.
Like previous example, but print .NH line as well as header title:
/^\.NH/{ N p }
Join two lines (replace newline with space):
/^\.NH/{ N s/\n/ / p }