.htaccess Rewrite issue. Possibly reserved words? - php

Question

This does not require much explanation, quite simply, how does the following work:
RewriteRule ^errors/browser/?$ /_errors/browser.php?error=browser [NC,QSA,L]
and this does not work:
RewriteRule ^error/browser/?$ /_errors/browser.php?error=browser [NC,QSA,L]
The only difference in two above snippets, is the removal of the letter s from the end of the word error
I cannot understand why the addition of an s on the word error suddenly makes this code work. The only explanation I can think of is that error is a reserved word? Is this the case?
If this is the case then how can I match and rewrite the word error using an .htaccess file?
UPDATE
This is my whole .htaccess file:
# Define the default document
DirectoryIndex index.php
# Turn on the rewrite engine
RewriteEngine On
# Compress all HTML, Javascript, CSS, XML... files
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript
# Set the error page rewrites
RewriteRule ^errors/browser/?$ /_errors/browser.php?error=browser [NC,QSA,L]
# Set the general first level rewrites
RewriteRule ^([a-z-]+)\/?$ $1.php? [NC,QSA,L]
RewriteRule ^([a-z-]+)\/([a-z-0-9]+)\/?$ $1.php?id=$2& [NC,QSA,L]

Answer 1

Quite strange that vim will highlight the word "error", but you may simply try this to hack it:
RewriteEngine On
RewriteRule ^erro[r]/index.html [NC,QSA,L]
And here is an issue maybe related: question-10872503