----------------------------------------
$string[no_data_string]
$pos[0]
index() FALSE
$pos[-1]
index() FALSE
----------------------------------------
$string[/DATA_String/]
$pos[0]
index() FALSE
$pos[-1]
index() TRUE
----------------------------------------
$string[X/DATA_String/]
$pos[0]
index() TRUE
$pos[-1]
index() TRUE
----------------------------------------
$string[/some/path/to/DATA_String/]
$pos[0]
index() TRUE
$pos[-1]
index() TRUE
----------------------------------------