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diff --git a/src/tools/clippy/src/docs/unsound_collection_transmute.txt b/src/tools/clippy/src/docs/unsound_collection_transmute.txt
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+### What it does
+Checks for transmutes between collections whose
+types have different ABI, size or alignment.
+
+### Why is this bad?
+This is undefined behavior.
+
+### Known problems
+Currently, we cannot know whether a type is a
+collection, so we just lint the ones that come with `std`.
+
+### Example
+```
+// different size, therefore likely out-of-bounds memory access
+// You absolutely do not want this in your code!
+unsafe {
+    std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
+};
+```
+
+You must always iterate, map and collect the values:
+
+```
+vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
+```
+\ No newline at end of file