>>> register = template.Library()
>>> @register.filter
... def undercat(value, len=None):
...     bits = value.split('<!--break-->')
...     if bits.__len__() == 2:
...         return '%s %s' % (bits[0], '')
...     return value
...
>>>
>>>
>>>
>>> undercat('asdasd')
'asdasd'
>>> undercat('asdasd<!--break-->jhasgdhgfasd')
'asdasd '