wp-includes/rewrite.php:351Filters the URL base for taxonomies.
$basestringstringfunction _wp_filter_taxonomy_base( $base ) { if ( ! empty( $base ) ) { $base = preg_replace( '|^/index\.php/|', '', $base ); $base = trim( $base, '/' ); } return $base;}Introduced in 2.6.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/rewrite.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.