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+### What it does
+Checks for all instances of `x + _` where `x` is of type
+`String`, but only if [`string_add_assign`](#string_add_assign) does *not*
+match.
+
+### Why is this bad?
+It's not bad in and of itself. However, this particular
+`Add` implementation is asymmetric (the other operand need not be `String`,
+but `x` does), while addition as mathematically defined is symmetric, also
+the `String::push_str(_)` function is a perfectly good replacement.
+Therefore, some dislike it and wish not to have it in their code.
+
+That said, other people think that string addition, having a long tradition
+in other languages is actually fine, which is why we decided to make this
+particular lint `allow` by default.
+
+### Example
+```
+let x = "Hello".to_owned();
+x + ", World";
+```
+
+Use instead:
+```
+let mut x = "Hello".to_owned();
+x.push_str(", World");
+```
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