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+# Vendoring for lit
+
+[lit](https://lit.dev/) can be used to help create Web Components.
+
+## The lit.all.mjs bundle
+
+The lit package is imported in a vendoring step and the contents are extracted
+into the lit.all.mjs file. This has some differences from using lit in a regular
+npm project. Imports that would normally be into a specific file are pulled
+directly from the lit.all.mjs file.
+
+eg.
+
+```
+// Standard npm package:
+import { LitElement } from "lit";
+import { classMap } from "lit/directives/class-map.js";
+
+// Using lit.all.mjs (pathing to lit.all.mjs may differ)
+import { classMap, LitElement } from "../vendor/lit.all.mjs";
+
+## To update the lit bundle
+
+Vendoring runs off of the latest tag in the https://github.com/lit/lit repo. If
+the latest tag is a lit@ tag then running the vendor command will update to that
+version. If the latest tag isn't for lit@, you may need to bundle manually. See
+the moz.yaml file for instructions.
+
+### Using mach vendor
+
+```
+./mach vendor toolkit/content/vendor/lit/moz.yaml
+hg ci -m "Update to lit@<version>"
+```
+
+### Manually updating the bundle
+
+To manually update, you'll need to checkout a copy of lit/lit, find the tag you
+want and manually run our import commands.
+
+  1. Clone https://github.com/lit/lit outside of moz-central
+  2. Copy *.patch from this directory into the lit repo
+  3. git apply *.patch
+  4. npm install && npm run build
+  5. Copy packages/lit/lit-all.min.js to toolkit/content/widgets/vendor/lit.all.mjs
+  6. hg ci -m "Update to lit@<version>"