class ActiveStorage::Attachment

def representation(transformations)

unknown pre-defined variant of the attachment.
Raises an +ArgumentError+ if +transformations+ is a +Symbol+ which is an

See ActiveStorage::Blob::Representable#representation for more information.

avatar.representation(:thumb).processed.url

or if you are using pre-defined variants:

avatar.representation(resize_to_limit: [100, 100]).processed.url

Example:
attachment with set of +transformations+ provided.
Returns an ActiveStorage::Preview or an ActiveStorage::Variant for the 
def representation(transformations)
  transformations = transformations_by_name(transformations)
  blob.representation(transformations)
end