Description:
------------
IntlChar::getNumericValue() will return a "magic number" of float(-123456789) if no numeric value exists for the given code point.  This behavior is correct and consistent with both the underlying library and HHVM's implementation.

However, the ICU library defines a constant for this magic number called U_NO_NUMERIC_VALUE, which we'd map to IntlChar::NO_NUMERIC_VALUE.  However, PHP does not expose this constant.  I believe this is a bug because both ICU and HHVM refer to a constant for this value, but we don't. (And magic numbers are bad.)

I would therefore request that this constant be added/exposed as IntlChar::NO_NUMERIC_VALUE.  This name will match the current naming conventions as well as the name used by HHVM.

(HHVM references this constant in the source but doesn't expose it - I've submitted a corresponding report here: https://github.com/facebook/hhvm/issues/6209)

If you disagree with my assessment that this is a bug, then I respectfully request this be changed to a Feature/Change Request.

Test script:
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See https://3v4l.org/48Bnh or run this yourself:

<?php

$value = IntlChar::getNumericValue("x");
var_dump($value);
var_dump($value === IntlChar::NO_NUMERIC_VALUE);

Expected result:
----------------
float(-123456789)
bool(true)

Actual result:
--------------
float(-123456789)

Fatal error: Uncaught Error: Undefined class constant 'NO_NUMERIC_VALUE' in /in/48Bnh:5
Stack trace:
#0 {main}
  thrown in /in/48Bnh on line 5

Process exited with code 255.