no allowable_content_types for description (avoid validation)

[tschorr]

Product.Archetypes.Field.validate invokes validate_content_types if allowable_content_types is set on a field. In case of the description field, this can lead to surprising validation results because the method is trying to guess the content type using the mimetypes_registry. Example: If you enter the word 'Stammdaten' (german for master data) as the first word into a description field, you see a validation error telling you that the MIME type 'video/quicktime' is not allowed for the field. This is because the mimetypes_registry is trying to guess the MIME type of the string 'Stammdaten' using a test in Products.MimetypesRegistry.mime_types.magic. The term 'Stammdaten' matches the following test pattern:

[4, 'string', '=', 'mdat', 'video/quicktime']

(letters 'mdat' starting at position4)

It is perfectly valid to have 'Stammdaten' as the first term in a german description, but Plone doesn't let you save this. Looking at the other test patterns there are potentially many more cases like this.

The testing procedure maybe could be improved (validating the content type is not about guessing the MIME type from the content but rather testing wether the content conforms to one of the allowable content types) but the suggestion is to simply drop the constraint on the description field since text/plain is the fallback.

[tschorr]

I have already signed the Plone Contributors Agreement and just added the email used for this PR to my account.

[gforcada]

@tschorr welcome to plone then! The checks are already updated as well :-)

[jensens]

@tschorr may you provide the same patch for master?