String search: the need for a "literal" pattern

[Dirk Laurie <dpl@...>]

In a certain string of length about 32000, a substring of length about 
900, running over several lines, occurs thirty-odd times.  Wishing to 
count the actual number of times, I cut-and-pasted it from another 
window into my Lua session:

    item = [[paste here]]

Then I tried:

    _,count = str:gsub(item,'')   

and got `count==0`.  Not expected.  Thinking there may have been
invisible characters, I tried this instead:

    item = str:sub(i,j)

having carefully found what i and j are.  Same result.

I soon discovered that the reason is that `item` contains several
magic characters.  

Quick workaround: devise a pattern that matches `item` and no other 
substring of `str`.  But nicer would be a pattern item that says: 
"treat the rest of this pattern as literal".  Say `%r`, for "raw".

Dirk