Retrieves one or more characters from the specified position in a string.
NewStr := SubStr(String, StartingPos , Length)
The string whose content is copied.
Specify 1 to start at the first character, 2 to start at the second, and so on (if StartingPos is beyond String's length, an empty string is returned). If StartingPos is less than 1, it is considered to be an offset from the end of the string. For example, 0 extracts the last character and -1 extracts the two last characters (but if StartingPos tries to go beyond the left end of the string, the extraction starts at the first character).
If this parameter is omitted, it defaults to "all characters". Otherwise, specify the maximum number of characters to retrieve (fewer than the maximum are retrieved whenever the remaining part of the string is too short). You can also specify a negative Length to omit that many characters from the end of the returned string (an empty string is returned if all or too many characters are omitted).
This function returns the requested substring of String.
Functionally, the SubStr function is almost the same as the StringMid command. However, it's recommended to use SubStr, because it is more flexible and future-proofed than StringMid.
RegExMatch(), StringMid, StringLeft/Right, StringTrimLeft/Right
Retrieves a substring with a length of 3 characters at position 4.
MsgBox % SubStr("123abc789", 4, 3) ; Returns abc