This question is not only about HTML and PHP, there are some files which are written in more than one language. Let's take example of HTML; here you can do CSS and JavaScript stuffs in it.
In Notepad++ you can make it possible with an extension (FingerText). It has choice to define language for the snippet where you can define more than one language and snippet from PHP will appear when working with HTML and vice-versa.
When I started using Ubuntu I was stick to its default text editor gedit, it has a good snippet manager. But the only problem is you can't do what you can do in Notepad++.
So, any other plugin? or Any gedit core file which I can edit to achieve this?