The .php file extension indicates a PHP page.
You can take any .html page, change the extension to .php, and the page is now ready to run PHP code.
PHP pages commonly include a mix of HTML and PHP code, although some PHP pages contain only PHP code, no HTML.
Any text inside a PHP page, but outside a PHP code island, is treated as HTML, just like a static web page (that is, a web page with the .htm or .html extension).
Editing PHP Pages
You can edit PHP pages using any text editor. While it is possible to edit PHP using a simple text editor, PHP developers commonly use Integrated Development Environment (IDE) programs such as Eclipse or Dreamweaver, because these programs provide [categorySeeAlso slug=”syntax-highlighting”] and other tools for working with PHP and HTML.