Sublime Text: Enable HTML code completion in Handlebars template script

Here are the steps necessary to enable the HTML code completion inside the <script type="text/x-handlebars"> tag when using Handlebars template in Sublime Text 3 ( and 2 ).

Install the PackageResourveViewer package for Sublime Text.

Open the Command Palette (Ctrl+Shift+P) and click on PackageResourveViewer: Open Resource
Click on HTML
Click on HTML.tmLanguage and the file will open

Search the string

<string>(?:^\s+)?(&lt;)((?i:script))\b(?![^&gt;]*/&gt;)</string>  

and replace with

<string>(?:^\s+)?(&lt;)((?i:script))\b(?!([^&gt;]*text/x-handlebars[^&gt;]*|[^&gt;]*/>))</string>`  

You are done: happy coding!