Introduce metadata for taxonomy terms.



Adds a new table to the database schema ( wp_termmeta ), and a set of

*_term_meta() API functions. get_terms() and wp_get_object_terms()

now also support 'meta_query' parameters, with syntax identical to other

uses of WP_Meta_Query .



When fetching terms via get_terms() or wp_get_object_terms() , metadata for

matched terms is preloaded into the cache by default. Disable this behavior

by setting the new $update_term_meta_cache paramater to false .



To maximize performance, within WP_Query loops, the termmeta cache is *not*

primed by default. Instead, we use a lazy-loading technique: metadata for all

terms belonging to posts in the loop is loaded into the cache the first time

that get_term_meta() is called within the loop.



Props boonebgorges, sirzooro.

See #10142.

