Axure: Max length characters in Repeaters

Sometimes I had problems with the max length characters. If they exceed the maximum character in a text field, we cant use the substring function:

-- Set Text on "txt_owner" equal to "[[item.owner.substring(0,7)]]"
if length of value of widget "txt_owner" is greater than "7"

where "txt_owner" is the name of the text field and "owner" is the name of the column in the "Repeater Dataset".

Source: Axure foum