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docs/tut/crash-course/13-strict-mode.md

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+# Strict Mode
+
+While developing UI with Vide, you should use Vide's strict mode, which can
+be set with `vide.strict = true` once when you first require Vide. Strict mode
+will add extra safety checks and emit better error traces, particularly when
+errors occur in property bindings.
+
+Strict mode is automatically enabled when Vide is required in O0 or O1
+optimization (default studio level). You can `vide.strict = false` if you do not
+want this.
+
+Strict mode will run derived sources and effects twice each time they update.
+This is to help ensure that derived source computations are pure, and that any
+cleanups made in derived sources or effects are done properly.
+
+```lua
+local source = vide.source
+local effect = vide.effect
+
+vide.strict = true
+
+local count = source(0)
+
+local ran = 0
+effect(function()
+    ran += 1
+end)
+
+print(ran) -- 2
+count(1)
+print(ran) -- 4
+```
+
+A full list of what strict mode will do can be found
+[here](../../api/strict-mode).