Full text search dev reference.

1.  OVERVIEW

	* All entities are searched through title and description using
	MySQL's native fulltext search when possible, and LIKE %...% when not.
	This can be overridden on a type/subtype basis.
	
	* Entities are displayed in a standard list view consisting of a 
	title, blurb, and icon of the owning entity.  This can be overridden 
	on a type/subtype basis.
	
	* Search is separated based upon types/subtypes pairs and any 
	registered custom search.
	
	* METADATA, ANNOTATIONS, AND PRIVATE DATA ARE NOT SEARCHED.  
	These are used in a variety of ways by plugin authors and generally 
	should not be displayed.  There are exceptions (profile fields and 
	comments) but if a plugin needs to match against metadata, 
	annotations, or private data it must register a search hook itself.


2.  SEARCH AND YOUR PLUGIN

	* To appear in search you must register your entity type and subtype
	by saying in your plugin's init function:
	
		register_entity_type($type, $subtype);
	
	If you are extending ElggObject with your own class, it is also advised 
	to add a subtype in your plugin's run_once function by saying:
	
		add_subtype($type, $subtype, $class);

	* If your plugin uses ElggEntity's standard title and description, 
	and you don't need a custom display, there is nothing else you need 
	to do for your results to appear in search.  If you would like more
	granular control of search, continue below.
	
	
3.1  CONTROLLING SEARCH -- ENTITIES

	* You can override the default search by responding to the search/type
	or search/type:subtype hook.  Generally, you will be replying to 
	search/object:subtype.

	* Search will first trigger a hook for search/type:subtype.  If no 
	results are returned (but not FALSE, see below) a hook for search/type 
	will be triggered.  
	
	* FALSE returned for any search hook will halt results for that type/subtype.
	
	* Register plugin hooks like this:
	
		register_plugin_hook('search', 'object:my_subtype', 'my_subtype_search_hook');
	
	* The hooked function is provided with details about the search query in $param.
	These include:
		query
		offset
		limit
		search_type
		type - Entity type. (Not applicable for custom searches)
		subtype - Entity subtype.  (Not applicable for custom searches)
		owner_guid
		friends - Should only entities by friends of the logged in 
			user be searched? (@todo)
		pagination - Show pagination?
	
	* The hooked function should respond to search triggers with the 
	following:
		array(
			'count' => A count of ALL entities found,
			'entities' => An array of entities.
		)
	
	This information is passed directly to the search view, so if you are 
	registering your own custom hook, you can provide more 
	information to display in your custom view. 
	
	* For each entity in the returned array, search expects two pieces of
	volatile data: search_matched_title and search_matched_description.
	Set these by saying:
	
		$entity->setVolatileData('data_name', 'data_value');
		
	Again, if you are customizing your search views, you can add anything
	you need.


3.2  CONTROLLING SEARCH - ENTITY VIEWS

	* The default view for entities is search/entity.

	* Search views are separate from the object/entity views because
	view types might not match entity types.
	
	* The default search listing view iterates through each entity
	found and passes to the entity view.  See 3.3 for more information
	about listing views.
	
	* Views are discovered in the following order.  The first search view 
	found is used.
		search/type/subtype/entity (For entity-based searches only)
		search/type/entity
		search/entity
		
	* The following parameters are passed in $vars to the entity view by 
	the default listing view:
		entity => The current returned entity
		results => The results from the search/type:subtype hook
		params => The params passed to the search/type:subtype hook
		
	* Example: To create an entity view for an ElggObject of subtype blog,
	create a file called:
		views/default/search/object/blog/entity.php
		
	To create an entity view for a custom search mysearch, create a file
	called:
		views/default/search/mysearch/entity.php
	
	
3.3  CONTROLLING SEARCH - LISTING VIEWS

	* The default search view is search/listing.
	
	* For each entity in the returned array, search expects two pieces of
	volatile data: search_matched_title and search_matched_description.
	
	* Views are discovered in the following order.  The first search view 
	found is used.
		search/type/subtype/listing (For entity-based searches only)
		search/type/listing
		search/listing
		
	* The view is called with the following in $vars:
		results => The results from the search/type:subtype hook
		params => The params passed to the search/type:subtype hook
		
	* Example: To create a listing view for ElggObjects with the subtype 
	of blog, create a file called:
		views/default/search/object/blog/listing.php
		
	To create a listing view for the custom search mysearch, create a file
	called:
		views/default/search/mysearch/listing.php


3.4  CONTROLLING SEARCH - CUSTOM SEARCH
	
	* Non-entities, including information from 3rd party applications,
	can easily be included in search by registering a custom search hook
	that responds to the search_types/get_types trigger:
	
		register_plugin_hook('search_types', 'get_types', 'my_custom_search_hook_function');
	
	In this function, append to the array sent in $value with the name of 
	your custom search:
	
		function my_custom_search_hook_function($hook, $type, $value, $params) {
			$value[] = 'my_custom_search';
			return $value;
		}
	
	Search will trigger a hook for search/my_custom_search, which your 
	plugin should respond to as detailed in section 3.1 above.


4.  HINTS

	* Use search_get_relevant_substring() to extract and highlight 
	relevant substrings for the search_match_title and description.
	
	* If searching in 3rd party applications, create a temporary 
	ElggObject to hold the results.  No need to save it since search 
	uses volatile data.
		$entity = new ElggObject();
		$entity->owner_guid = use_magic_to_match_to_a_real_user();
		$entity->setVolatileData('search_matched_title', '3rd Party Integration');
		$entity->setVolatileData('search_matched_description', 'Searching is fun!');
		
		return array(
			'count' => $count,
			'entities' => array($entity)
		);