strings.SliceString

The START and END positions are zero-based, where 0 represents the first character of the string. If START is not specified, the substring will begin at position 0. If END is not specified, the substring will end after the last character.

{{ slicestr "BatMan" }} → BatMan
{{ slicestr "BatMan" 3 }} → Man
{{ slicestr "BatMan" 0 3 }} → Bat

The START and END arguments represent the endpoints of a half-open interval, a concept that may be difficult to grasp when first encountered. You may find that the strings.Substr function is easier to understand.