The documentation of the built-in template tag truncatechars did not yet have the Django version (1.4) which can cause confusion for those using Django 1.3 and earlier.
This pull request adds that.
Added Django version to truncatechars template tag documentation
It wasn't clear to me whether a ticket was needed for this so I have opened one here: https://code.djangoproject.com/ticket/20381 - please close it when merging in.
See comment on the ticket.