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The best way to understand what a hook does is to look at where it occurs in the source code.
do_action( "hook_name" )apply_filters( "hook_name", "what_to_filter" ).Remember, this hook may occur in more than one file. Moreover, the hook's context may change from version to version.
| Line | Code |
|---|---|
| 175 | * |
| 176 | * @param null|bool $check Whether to allow updating metadata for the given type. |
| 177 | * @param int $object_id Object ID. |
| 178 | * @param string $meta_key Meta key. |
| 179 | * @param mixed $meta_value Meta value. Must be serializable if non-scalar. |
| 180 | * @param mixed $prev_value Optional. If specified, only update existing |
| 181 | * metadata entries with the specified value. |
| 182 | * Otherwise, update all entries. |
| 183 | */ |
| 184 | $check = apply_filters( "update_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $prev_value ); |
| 185 | if ( null !== $check ) |
| 186 | return (bool) $check; |
| 187 | |
| 188 | // Compare existing value to new value if no prev value given and the key exists only once. |
| 189 | if ( empty($prev_value) ) { |
| 190 | $old_value = get_metadata($meta_type, $object_id, $meta_key); |
| 191 | if ( count($old_value) == 1 ) { |
| 192 | if ( $old_value[0] === $meta_value ) |
| 193 | return false; |