[wp-trac] [WordPress Trac] #64991: New param "allow_multiple_terms" in `register_taxonomy` for single term restriction

[WordPress Trac]

#64991: New param "allow_multiple_terms" in `register_taxonomy` for single term
restriction
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 Reporter:  bastho           |      Owner:  (none)
     Type:  feature request  |     Status:  new
 Priority:  normal           |  Milestone:  Awaiting Review
Component:  Taxonomy         |    Version:
 Severity:  normal           |   Keywords:
  Focuses:  ui               |
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 The `register_taxonomy` function is based on the two main taxonomies:
 categories and tags.

 Custom taxonomies can only have those two behaviors: hierarchical terms,
 like categories or non hierarchical terms like tags.

 At this time, when a plugin adds a custom taxonomy, the generated UI is:
 - checkboxes for category like taxonomies
 - multiple select  for tag like taxonomies

 If a plugin needs to exclusive terms, the UI has to be hidden and a custom
 box added which causes UI inconsistency between plugins.

 It would be very useful to natively allow single term behavior, just like
 post-format does.
 In this case, the UI could be a simple **select** or **radio buttons**
 (preference for select).


 I suggest a `allow_multiple_terms` parameter, with default value **true**

 Setting it to **false** would make use the simple `<select>` field.

 Caveats:
 Need to manage: single edit page, quick-edit and bulk-edit.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64991>
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