New recipe: Case-insensitivity

hugo/content/docs/recipes/lexis/_index.md

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+---
+title: Lexis
+weight: 100
+---

hugo/content/docs/recipes/lexis/case-insensitive-languages.md

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+---
+title: Case-insensitive languages
+weight: 100
+---
+
+Case-insensitive languages are more suitable for beginners, because they don't have to worry about the case of identifiers and keywords.
+
+In Langium, there are basically two options you can choose from:
+
+* you can either make Langium case-insensitive by configuration
+* or you can include case-insensitivity only where you need it
+
+In both ways you need to take care of identifiers and cross-references.
+
+## Case-insensitivity by Langium
+
+To make Langium case-insensitive, you have to set the `caseInsensitive` option to `true` in the `LangiumConfig` object which is located in the `langium-config.json` file at the root of your Langium project. You can set this up for every single language.
+
+```json
+{
+    "projectName": "HelloWorld",
+    "languages": [{
+        "id": "hello-world",
+        "caseInsensitive": true, //here
+        //...
+    }],
+    //...
+}
+```
+
+## Case-insensitivity on demand
+
+If you want to include case-insensitivity only where you need it, you can use the `i` flag inside of your grammar's regular expressions
+
+```ts
+//instead of
+Rule: 'keyword';
+//use
+Rule: /keyword/i;
+```
+
+## Case-insensitivity for identifiers and cross-references
+
+But be aware of that both ways will only take care of all the keywords in your grammar. If you want identifiers and cross-references to be case-insensitive as well, you have to adjust your scoping for each cross-reference case. This can be accomplished by setting the `caseInsensitive` option to `true` within the options when you are creating a new scope object.
+
+There are several implementations of scopes. One is `MapScope`:
+
+```ts
+new MapScope(descriptions, parentScope, {caseInsensitive: true});
+```