substr() returns the portion of
string specified by the start and length parameters.
If start is
non-negative, the returned string will start at the start'th position in string, counting from zero. For
instance, in the string 'abcdef',
the character at position 0 is 'a', the character at position 2 is 'c', and so
forth.
If start is negative,
the returned string will start at the
start'th character from the end of string.
If length is given and
is positive, the string returned will contain at most length characters beginning
from start (depending on
the length of string). If
string is less than start characters long, FALSE will be returned.
If length is given and
is negative, then that many characters will be omitted from
the end of string (after
the start position has been calculated when a start is negative). If start denotes a position beyond this
truncation, an empty string will be returned.