can I use a category as common for more than one custom post types? In this case same category will have more than one type of posts..
When you use
register_taxonomy(), the second argument is the
object_type argument, which accepts either a string or an array. You can pass this an array of objects to apply the taxonomy to, and it will be common between those. So, for example:
array( 'cpt_slug', 'post' ) would give you a common taxonomy between
If you want to add the existing taxonomies to a new post type, you can use