Updated syntax, corrected and added information. (#19433)

Updated syntax to adhere to PSR, corrected outdated information, and added additional information regarding tags and indentation.

client/src/pages/guide/english/php/php-syntax-and-comments/index.md

@@ -2,42 +2,65 @@
 title: PHP Syntax and Comments
 ---
 
-### PHP Syntax
+## PHP Syntax
 
-The structure of a PHP syntax somewhat looks like:
+The structure of a PHP document may look something like:
 
-```shell
-    <?php
-    
-    // Your PHP code goes here.
-    
-    ?>
 ```
-This PHP script can be placed anywhere in the document.
-A PHP file generally have HTML tags, and some scripting code .
-The default file extension for PHP files is `.php`.
- 
- ### How to make comments in PHP?
- 
-A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is looking at the code.
+<?php
+    
+// Your PHP code goes here.
+```
 
-In PHP, comments can be make by two ways either single lined or multi-lined.
-The code snippet given below explains it:
+**NOTE:** When creating a document with only PHP, the closing tags (see below) should be omitted.
 
-```shell
-<?
-   // This is a single-line comment
+When placing PHP in an HTML document, a closing tag is needed, like so:
 
-    # This is also a single-line comment
+```
+<?php
+
+// Your PHP code goes here.
 
-   /*
-     This is a multiple-lines comment block
-     that spans over multiple
-     lines
-   */
 ?>
 ```
 
-### More information
+**NOTE:** Shorthand syntax is also available, but should be avoided to reduce unwanted behavior.
 
-For more resources you can visit: https://www.w3schools.com/php/php_syntax.asp
+A PHP file may have HTML tags and / or JavaScript.
+
+The default file extension for PHP files is `.php`.
+
+## Indentation
+
+While this is mostly personal preference, it is most common to see the lines within the <?php / ?> tags at the same level, like so:
+
+```
+<?php
+
+// Same level of indendation.
+    // Not indented like so.
+```
+ 
+## How to make comments in PHP?
+ 
+A comment in PHP code is a line that is not executed as part of the program. Its only purpose is to be read by someone who is looking at the code.
+
+In PHP, comments can be make by two ways — either single-lined or multi-lined.
+
+This can be seen in the example below:
+
+```
+<?
+
+// This is a single-lined comment.
+
+/**
+ * This is a multi-lined comment block
+ * that spans over multiple
+ * lines.
+ */
+```
+
+## Additional Information
+
+For more information, please see [PHP: Comments](http://php.net/manual/en/language.basic-syntax.comments.php).