title: How to start creating a language extension for VS Code?
body: <p>Pursuant to the discussion in <a href="https://github.com/microsoft/vscode/issues/111447" rel="nofollow noreferrer">Add XHTML support</a>, I'd like to start creating an extension for Visual Studio Code which would implement support for XHTML. Which is HTML with XML syntax, so the the desired functionality is already (mostly?) implemented elsewhere – for XML and HTML languages, the latter having two extensions bundled with VS Code: <code>html</code> and <code>html-language features</code>. But it's disparate.</p>
  <p>As the first step, should I clone the VS Code repo and delete everything except the two directories named <code>html</code> and <code>html-language features</code>? Or <a href="https://github.com/microsoft/vscode-html-languageservice" rel="nofollow noreferrer">Language services for HTML</a>? Or the latter and <code>html</code> from the former? Or start with <code>html</code>, make it work for XHTML and only then deal with language features?</p>
  <p>Should the second step be just adding the extension(s) I'm developing on my computer to my installation of VS Code? The GUI seems to allow adding only extensions from the Visual Studio Marketplace. Is it the right solution to place the extensions under development into VS Code's directory for extensions (either directly or with symbolic links)? I'm on Manjaro Linux.</p>
  <p>If you can offer any other helpful advice, I welcome it too.</p>