Add ast extension

DOCUMENTATION/content/documentation/index.md

@@ -1973,6 +1973,26 @@ YAML PHP extension allows you to easily parse and create YAML structured data. I
 4 - Re-build the container `docker-compose build php-fpm`<br>
 
 
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+<br>
+<a name="Install-AST"></a>
+## Install AST PHP extension
+AST exposes the abstract syntax tree generated by PHP 7+. This extension is required by tools such as `Phan`, a static analyzer for PHP.
+
+1 - Open the `.env` file
+
+2 - Search for the `WORKSPACE_INSTALL_AST` argument under the Workspace Container
+
+3 - Set it to `true`
+
+4 - Re-build the container `docker-compose build workspace`
+
+**Note** If you need a specific version of AST then search for the `WORKSPACE_AST_VERSION` argument under the Workspace Container and set it to the desired version and continue step 4.
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 <a name="phpstorm-debugging"></a>
 ## PHPStorm Debugging Guide