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function is not described

path_is_absolute() WP 2.5.0

Test if a given filesystem path is absolute.

For example, '/foo/bar', or 'c:\windows'.

No Hooks.

Return

true/false. True if path is absolute, false is not absolute.

Usage

path_is_absolute( $path );
$path(string) (required)
File path.

Code of path is absolute: wp-includes/functions.php VER 5.0.3

<?php
function path_is_absolute( $path ) {
	/*
	 * This is definitive if true but fails if $path does not exist or contains
	 * a symbolic link.
	 */
	if ( realpath($path) == $path )
		return true;

	if ( strlen($path) == 0 || $path[0] == '.' )
		return false;

	// Windows allows absolute paths like this.
	if ( preg_match('#^[a-zA-Z]:\\\\#', $path) )
		return true;

	// A path starting with / or \ is absolute; anything else is relative.
	return ( $path[0] == '/' || $path[0] == '\\' );
}