php - Why does product_tag_edit_form_fields action works in woocommerce? -

i total newbie woo-commerce. please bear me if use incorrect terminology or ask stupid.

i trying add custom field product tags. able find articles showed how-to add custom filed product category instead (http://www.wpmusketeer.com/add-a-wysiwyg-field-to-woocommerce-product-category-page/).

i modified actions in tutorial , replaced product_cat_edit_form_fields product_tag_edit_form_fields, edited_product_cat edited_product_tag , on. , worked well! able add/edit new field in product tags.

but can't find action documented anywhere when google out. can tell me why working well?