Subtracts a year from a date. The value must be of the form {{Y,M,D},{H,I,S}}.
For example:
{{ value|sub_year }}
When the value is {{2008,12,10},{15,30,0}} then the output is {{2007,12,10},{15,30,0}}.
The filter has an optional argument which defines the number of years to subtract:
For example:
{{ value|sub_year:3 }}
When the value is {{2008,12,10},{15,30,0}} then the output is {{2005,12,10},{15,30,0}}.