html 中是否有类似 '\\f' 的实体？

Question

I was simply outputting a string using echo in php but it got altered and its not showing the exact string.I know about HTML entities little bit but not aware of anything called \\f entity in HTML, or is something else causing the issue

<?php


$orig = "&lt;math&gt;x^2 \frac{d^2 y}{dx^2} + x \frac{dy}{dx} + (x^2 - \alpha^2)y = 0&lt;/math&gt;";

echo $orig;


?>

and the output is

<math>x^2 rac{d^2 y}{dx^2} + x rac{dy}{dx} + (x^2 - \alpha^2)y = 0</math>

Hope you noticed \\frac changed to rac.What might be the issue ?

Answer 1

\\f is actually a formfeed in many languages although it's rarely used. It's php, not html, that reads the string and changes it. You can read about it here: http://php.net/manual/en/regexp.reference.escape.php

Can you simply add a Space between \\ and frac ?

Answer 2

Just put &#92 instead of the backslash itself and you should have no problem. Example &#92frac