Apache 2.4 provides the following 6 directives via the mod_rewrite module:

1. RewriteBase
2. RewriteCond
3. RewriteEngine
4. RewriteMap
5. RewriteOptions
6. RewriteRule

The following directives, available previously in Apache 2.2 have been removed:

1. RewriteLock
2. RewriteLog
3. RewriteLogLevel

All the directives (with the exception of RewriteMap) defined by mod_rewrite can be allowed to override on a per-directory .htaccess through the AllowOverride FileInfo.

Directive	Context	Description
RewriteBase	directory, .htaccess	Sets base URL for per directory rewrite
RewriteCond	Everywhere	Defines conditions under which the rewrite action will occur
RewriteEngine	Everywhere	Sets status of rewrite engine
RewriteMap	server config, virtual host	Defines a key lookup function
RewriteOptions	Everywhere	Sets special options for rewrite engine
RewriteRule	Everywhere	Defines specific rules for rewrite engine

The context Everwhere means that the directive can be defined in any of the following four locations:

1. server config
2. virtual host config
3. directory context
4. .htaccess file

The RewriteLog and RewriteLogLevel directives have been merged with the global LogLevel directive and would be used as:

LogLevel rewrite:<level>

where <level> is a value from trace8 (least significant) to emerg (most significant). This list is available here.

Directive	Default	Context	Description
RewriteBase	None	Directory, .htaccess	Sets base URL for per directory rewrite
RewriteEngine	off	everywhere	Enable or disable runtime rewrite engine

RewriteBase

The directive specifies URL prefix to be used for substituting relative paths.

RewriteEngine

The directive, if set to off, will perform no runtime rewrite processing. These rules are not inherited by the virtual hosts (from server config), and will have to be defined individually.

The directive defines a function which'll lookup a key in the defined map and substitutes the lookup with its replacement from the map.

The mapping function is defined with the RewriteMap directive itself as follows:

RewriteMap MAPNAME Type:Source

and can be referenced in any of the RewriteCond or RewriteRule directives to act as a substitution guide as follows:

${ MAPNAME : KEY | DEFAULT }

The following are valid values for Type in the map definition:

1. int - allows toupper, tolower, escape and unescape only
2. txt - searches a text file
3. dbd - looks up in a database using SQL SELECT statement
4. rnd - random lookups from text file
5. dbm - similar to txt, except that the httxt2dbm needs to convert the data to hashes
6. fastdbd - looks up in a database using SQL SELECT statement with caching