Description:
------------
The manual says in "Comparison Operators":

> If [..] the comparison involves numerical strings, then each string is 
> converted to a number and the comparison performed numerically.

That does explain why e.g. "10" == "0xa" evaluates to true. Now I would expect that every other representation of 10 would do the same. It doesn't for binary and octal representations. I.e "10" == "0b1010" evaluates to false, the same for "10" == "012".

One could argue that numerical string is not defined. But then I would expect that a string for which is_numeric() returns true would qualify as a numerical string. is_numeric("012") does return true, but "012" == "10" not.

Test script:
---------------
<?php

var_dump(
    0b1010, "10" == "0b1010", // false
    012,    "10" == "012",    // false
    0xa,    "10" == "0xa",    // true
    1E+1,   "10" == "1E+1",   // true
    1e1,    "10" == "1e1",    // true
    10.0,   "10" == "10.0",   // true
    +10,    "10" == "+10"     // true
);

Expected result:
----------------
int(10)
bool(true)
int(10)
bool(true)
int(10)
bool(true)
double(10)
bool(true)
double(10)
bool(true)
double(10)
bool(true)
int(10)
bool(true)

Actual result:
--------------
int(10)
bool(false)
int(10)
bool(false)
int(10)
bool(true)
double(10)
bool(true)
double(10)
bool(true)
double(10)
bool(true)
int(10)
bool(true)