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docs/tut/crash-course/6-root.md

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+# Root Reactive Scopes
+
+Any reactive scopes created, such as one from `effect()`, must be done so within
+a "root" reactive scope. This is the main purpose of `mount()`, which you use
+once at the top level to create your app as shown in the first introduction.
+
+This is so that when the app is unmounted, it can clean up any reactive scopes
+created within it, since reactive scopes track any reactive scopes created
+within them.
+
+```lua
+local source = vide.source
+local effect = vide.effect
+
+local function App()
+    local count = source(0)
+
+    effect(function()
+        print(count())
+    end)
+end
+
+vide.mount(App) -- works!
+
+App() -- will error since effect() was not called within a reactive scope
+```
+
+The reactive graph for the above example:
+
+```mermaid
+%%{init: {
+    "theme": "base",
+    "themeVariables": {
+        "primaryColor": "#1B1B1F",
+        "primaryTextColor": "#fff",
+        "primaryBorderColor": "#1B1B1F",
+        "lineColor": "#79B8FF",
+        "tertiaryColor": "#161618",
+        "tertiaryBorderColor": "#161618"
+    }
+}}%%
+
+flowchart
+
+subgraph root
+    direction LR
+    count --> effect
+end
+```