mb_substr() returns the portion of str specified by the start and length parameters.
mb_substr() performs multi-byte safe substr() operation based on number of characters. Position is counted from the beginning of str. First character's position is 0. Second character position is 1, and so on.
If encoding is omitted, internal encoding is assumed.
encoding is character encoding. If it is omitted, internal character encoding is used.
See also mb_strcut(), mb_internal_encoding().