Finds the length of the initial segment of a string consisting entirely of characters contained within a given mask
strspn ( string $subject , string $mask [, int $start [, int $length ]] ) : int
The string to examine.
The list of allowable characters.
The position in subject to start searching. If start is given and is non-negative, then strspn() will begin examining subject at the start'th position. 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 given and is negative, then strspn() will begin examining subject at the start'th position from the end of subject.
The length of the segment from subject to examine. If length is given and is non-negative, then subject will be examined for length characters after the starting position. If length is given and is negative, then subject will be examined from the starting position up to length characters from the end of subject.
Returns the length of the initial segment of subject which consists entirely of characters in mask.
Note: When a start parameter is set, the returned length is counted starting from this position, not from the beginning of subject.
START | NEGATIVE
START | NON-NEGATIVE
LENGTH | NEGATIVE
LENGTH | NON-NEGATIVE