This RFC proposes to remove support for hexadecimal numers in is_numeric_string . Support for hex in this function is inconsistent with behavior in other places - in particular PHP does not detect hex numbers when performing integer or float casts.

PHP internally has two primary methods from converting strings into numbers:

The first, and most commonly used, are direct casts to the integer or float types ( convert_to_long and convert_to_double ). These casts do NOT support hexadecimal numbers:

The second possibility is the is_numeric_string function, which will convert a string to either an integer or a float, whichever is more appropriate. This function does support hexadecimal numbers.