Returns the first position of a search argument from the end of source string, or 0 if it was not found. The first character in the string is considered position 1.
Parameters
- Value to look for
- Index to start from (optional) - if omitted, search starts from the end of the string; index 1 is considered the first character in the string
- Length to search (optional) - if omitted, the rest of the string is searched
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