Search across multiple lines

==Patterns including end-of-line==
The search <code>/^abcd</code> finds <code>abcd</code> at the beginning of a line, and <code>/abcd$</code> finds <code>abcd</code> at the end of a line. However, in <code>/abcd^efgh</code> and <code>/abcd$efgh</code> the <code>^</code> and <code>$</code> are just ordinary characters with no special meaning. By contrast, each of the following has a special meaning anywhere in a search pattern.

{| class="cleartable"
| <code>\n</code> || a newline character (line ending)
|-
| <code>\_s</code> || a whitespace (space or tab) or newline character
|-
| <code>\_^</code> || the beginning of a line (zero width)
|-
| <code>\_$</code> || the end of a line (zero width)
|-
| <code>\_.</code> || any character including a newline
|}

Example searches:
;<code>/abcd\n*efgh</code>
:Finds <code>abcd</code> followed by zero or more newlines then <code>efgh</code>.
:Finds <code>abcdefgh</code> or <code>abcd</code> followed by blank lines and <code>efgh</code>.
:The blank lines have to be empty (no space or tab characters).

;<code>/abcd\_s*efgh</code>
:Finds <code>abcd</code> followed by any whitespace or newlines then <code>efgh</code>.
:Finds <code>abcdefgh</code> or <code>abcd</code> followed by blank lines and <code>efgh</code>.
:The blank lines can contain any number of space or tab characters.
:There may be whitespace after <code>abcd</code> or before <code>efgh</code>.

;<code>/abcd\_$\_s*efgh</code>
:Finds <code>abcd</code> at end-of-line followed by any whitespace or newlines then <code>efgh</code>.
:There must be no characters (other than a newline) following <code>abcd</code>.
:There can be any number of space, tab or newline characters before <code>efgh</code>.

;<code>/abcd\_s*\_^efgh</code>
:Finds <code>abcd</code> followed by any whitespace or newlines then <code>efgh</code> where <code>efgh</code> begins a line.
:There must be no characters (other than a newline) before <code>efgh</code>.
:There can be any number of space, tab or newline characters after <code>abcd</code>.

;<code>/abcd\_$efgh</code>
:Finds nothing because <code>\_$</code> is "zero width" so the search is looking for <code>abcdefgh</code> where <code>abcd</code> is also at end-of-line (which cannot occur).

;<code>/abcd\_^efgh</code>
:Finds nothing because <code>\_^</code> is "zero width" so the search is looking for <code>abcdefgh</code> where <code>efgh</code> is also at beginning-of-line (which cannot occur).

;<code>/abcd\_.\{-}efgh</code>
:Finds <code>abcd</code> followed by any characters or newlines (as few as possible) then <code>efgh</code>.
:Finds <code>abcdefgh</code> or <code>abcd</code> followed by any characters then <code>efgh</code>.

;<code>/abcd\(\_s.*\)\{0,18\}\_sefgh</code>
:Finds a block of 0 to 18 lines enclosed by <code>abcd</code> and <code>efgh</code>.
:limiting the number of lines is important, replacing this by a star will cause vim to consume 100% CPU.