Vimpager script: Highly mysterious - vim

Question

I have switched my pager from less to vimpager because vim responds to the mouse wheel.
However recently after updating my vim setup by compiling a newer version of vim 7.3, and adding a series of awesome plugins, vimpager no longer does anything logical when I attempt to search text in a manpage using n and N.
This is really bad so I set out to trace the bindings back using :verbose map.
From the vimpager script (/usr/local/share/vim/vim73/macros/less.vim):
" Search
noremap <script> / H$:call <SID>Forward()<CR>/
if &wrap
noremap <script> ? H0:call <SID>Backward()<CR>?
else
noremap <script> ? Hg0:call <SID>Backward()<CR>?
endif
fun! s:Forward()
" Searching forward
noremap <script> n H$nzt<SID>L
if &wrap
noremap <script> N H0Nzt<SID>L
else
noremap <script> N Hg0Nzt<SID>L
endif
cnoremap <silent> <script> <CR> <CR>:cunmap <lt>CR><CR>zt<SID>L
endfun
fun! s:Backward()
" Searching backward
if &wrap
noremap <script> n H0nzt<SID>L
else
noremap <script> n Hg0nzt<SID>L
endif
noremap <script> N H$Nzt<SID>L
cnoremap <silent> <script> <CR> <CR>:cunmap <lt>CR><CR>zt<SID>L
endfun
call s:Forward()
" Quitting
noremap q :q<CR>
That last one I get and it makes a lot of sense. But this H$nzt<SID>L is completely impenetrable.
What the hell is it doing?
P.S. I've gotten my search back by turning those two functions s:Forward() and s:Backward() into empty no-op functions. So I'm all set, but what does that stuff do?

Answer 1

You can use the scrollwheel in less.
Anyway…
H "puts the cursor on the first printable character
"of the first visible line of the window.
$ "moves the cursor to the end of that line
n "moves the cursor on the next match
zt "scrolls the current line at the top of the window
<SID>L "executes the L mapping defined in the current script
The whole thing looks like a slightly convoluted attempt to make Vim's n work like less's n.