All ManyToMany field get a default message which is not overridable

[Anand Kumria]

All ManyToManyFields get a default message in the help_text, which is not overridable.

The message is: 'Hold down "Control", or "Command" on a Mac, to select more than one.'

This is done in the file django/db/models/fields/related.py and it makes sense if the related field is being displayed as a select list.

However, if you display a many to many relation using the inbuilt CheckboxSelectMultiple widget - for example - the message actually makes no sense. It makes no sense because you will have multiple checkboxes which you can independently click on.

In fact, have a textual string referencing the likely output method in the model seems to be a layering violation.

Attached is a patch to put this text in only if there is no help_text provided. Since it will use the overridden help_text, people are free to add back in the initial text if required.

[anonymous]

This is #9321.