strrpos() function compare two strings, return the last occurrence position of the 2nd string inside the 1st string. If the 1st string do not contain the 2nd string, return FALSE.

<?PHP
	echo strrpos("The best time is no time at that time","time");  //33
	if (strrpos("The best time is no time at that time","PHP"))
	{
	   echo "contain PHP";
	}
	else echo "do not contain PHP";
	//do not contain PHP
	echo strrpos("The best time is no time at that time","The");  //0
?>

strrpos() function is case sensitive.

<?PHP
	if (strrpos("The best time is no time at that time","TIME"))
	{
	   echo "contain TIME";
	}
	else echo "do not contain TIME";
	//do not contain TIME
	if (strrpos("The best time is no time at that time","time"))
	{
	   echo "contain time";
	}
	else echo "do not contain time";
	//contain time
?>

If the occurrence position is the 1st character position, will return 0. That may cause wrong results when used in a condition statement.

<?PHP
	if (strrpos("The best time is no time at that time","The"))
	{
	   echo "contain The";
	}
	else echo "do not contain The";
	//do not contain The
?>

The correct statement is:

<?PHP
	if (strrpos("The best time is no time at that time","The") === FALSE)
	{
	   echo "do not contain The";
	}
	else echo "contain The";
	//contain The
?>