Merge pull request #475 from WebAssembly/elaborate-structured-control…

…-flow

Clarify well-structured control flow

AstSemantics.md

@@ -250,9 +250,15 @@ Branches that exit a `block`, `loop`, or `tableswitch` may take a subexpression
 that yields a value for the exited construct.
 Branches may only reference labels defined by an outer *enclosing construct*.
 This means that, for example, references to a `block`'s label can only occur 
-within the `block`'s body. In practice, outer `block`s can be used to place labels for any
-given branching pattern, except for one restriction: one can't branch into the middle of a
-loop from outside it. This restriction ensures all control flow graphs are well-structured.
+within the `block`'s body.
+
+In practice, outer `block`s can be used to place labels for any given branching
+pattern, except for one restriction: one can't branch into the middle of a loop
+from outside it. This restriction ensures all control flow graphs are well-structured
+in the exact sense as in high-level languages like Java, JavaScript, Rust and Go. To
+further see the parallel, note that a `br` to a `block`'s label is functionally
+equivalent to a labeled `break` in high-level languages in that a `br` simply
+breaks out of a `block`.
 
 ### Yielding values from control constructs