What does the search function in Magento actually search for?

Question

When I do a search for 999 I get 11 items, 10 of which does not have 999 in their name, at first I thought maybe the search also looks at their descriptions but there is no 999 in the other 10's descriptions either.

So I was wondering what other attributes the search function in magento actually looks at to bring up the results.

I should also note that all these items are configurable products and the simple products associated with them have roughly the exact same data but have different SKUs and their names also have their size in them (though none of the sizes are 999)

Answer 1

When defining attributes for products you can mark them as 'Searchable'. The search is performed on the attributes marked like that.
The values of these attributes are aggregated in the table catalogsearch_fulltext.
Maybe the '999' value is in on of the attributes that you don't know is searchable.
You can identify the search-able attributes with this query:

select a.*, b.* from eav_attribute a inner join catalog_eav_attribute b on a.attribute_id = b.attribute_id where b.is_searchable = 1