Merge pull request #315 from kevanstannard/syntax-lookup-open

Syntax lookup: Open

Author: ryyppy

misc_docs/syntax/language_open.mdx

@@ -0,0 +1,35 @@
+---
+id: "open"
+keywords: ["open", "module"]
+name: "open"
+summary: "This is the `open` keyword."
+category: "languageconstructs"
+---
+
+`open` is used to expose all values, types, modules, etc of a module in the current scope. This is useful whenever you want to use a module's functionality without typing out the module name over and over again.
+
+In some cases, `open` will cause a "shadow warning" due to existing identifiers and types being redefined by an `open`ed module. You can explicitly ignore that warning by using an `open!` statement instead.
+
+### Example
+
+<CodeTab labels={["ReScript", "JS Output"]}>
+
+```res
+open Js.Math
+
+// Use _PI and pow_float from the Js.Math module
+let area = radius => _PI *. pow_float(~base=radius, ~exp=2.0)
+```
+
+```js
+function area(radius) {
+  return Math.PI * Math.pow(radius, 2.0);
+}
+```
+
+</CodeTab>
+
+### References
+
+* [Opening a module](/docs/manual/latest/module#opening-a-module)
+* [Use open! to ignore shadow warnings](/docs/manual/latest/module#use-open-to-ignore-shadow-warnings)