RewriteEngine on 
RewriteBase /textfiles/

# Send requests without parameters to textfiles.php.
# RewriteRule ^$ textfiles.php  [L]

# Send requests for index.php to textfiles.php.
# RewriteRule ^index\.php$ textfiles.php  [L]

# Send requests for index.html to textfiles.php.
# RewriteRule ^index\.html$ textfiles.php  [L]

# Send requests for textfiles.css to textfiles.css.
RewriteRule ^textfiles\.css$ textfiles.css  [L]

# Send requests for textfiles.js to textfiles.js.
RewriteRule ^textfiles\.js$ textfiles.js  [L]

# Send requests for textfiles.php to textfiles.php.
RewriteRule ^textfiles\.php$ textfiles.php  [L]

# Send requests for textfiles.html to textfiles.php.
# NOTE: THIS IS NOT A TYPO!
RewriteRule ^textfiles\.html$ textfiles.php  [L]

# Send requests for files that exist to textfiles.php (raw).
RewriteCond %{REQUEST_URI} ^\/textfiles\/(.+)/raw$
RewriteCond /file/path/to/your/textfiles/%1 -f
RewriteRule ^(.+)/raw$ textfiles.php?f=$1&m=raw [QSA,L]

# Send requests for files that exist to textfiles.php.
RewriteCond %{REQUEST_URI} ^\/textfiles\/(.+)$
RewriteCond /file/path/to/your/textfiles/%1 -f
RewriteRule ^(.+)$ textfiles.php?f=$1 [QSA,L]