Move select out of the "control flow opcodes" section.

AstSemantics.md

@@ -1,14 +1,19 @@
 # Abstract Syntax Tree Semantics
 
-WebAssembly code is represented as an Abstract Syntax Tree (AST) where each node
-represents an expression. Each function body consists of a list of expressions.
-All expressions and operators are typed, with no implicit conversions or overloading rules.
+This document describes WebAssembly semantics. The description here is written
+in terms of an Abstract Syntax Tree (AST), however it is also possible to
+understand WebAssembly semantics in terms of a stack machine. (In practice,
+implementations need not build an actual AST or maintain an actual stack; they
+need only behave [as if](https://en.wikipedia.org/wiki/As-if_rule) they did so.)
 
 This document explains the high-level design of the AST: its types, constructs, and
 semantics. For full details consult [the formal Specification](https://github.com/WebAssembly/spec),
 for file-level encoding details consult [Binary Encoding](BinaryEncoding.md),
 and for the human-readable text representation consult [Text Format](TextFormat.md).
 
+Each function body consists of a list of expressions. All expressions and
+operators are typed, with no implicit conversions or overloading rules.
+
 Verification of WebAssembly code requires only a single pass with constant-time
 type checking and well-formedness checking.
 

BinaryEncoding.md

@@ -326,17 +326,16 @@ It is legal to have several entries with the same type.
 
 | Name | Opcode | Immediates | Description |
 | ---- | ---- | ---- | ---- |
-| `nop` | `0x00` | | no operation |
+| `unreachable` | `0x00` | | trap immediately |
 | `block` | `0x01` |  | begin a sequence of expressions, the last of which yields a value |
 | `loop` | `0x02` |  | begin a block which can also form control flow loops |
 | `if` | `0x03` | | begin if expression |
 | `else` | `0x04` | | begin else expression of if |
-| `select` | `0x05` | | select one of two values based on condition |
 | `br` | `0x06` | argument_count : `varuint1`, relative_depth : `varuint32` | break that targets an outer nested block |
 | `br_if` | `0x07` | argument_count : `varuint1`, relative_depth : `varuint32` | conditional break that targets an outer nested block |
 | `br_table` | `0x08` | see below | branch table control flow construct |
 | `return` | `0x09` | argument_count : `varuint1` | return zero or one value from this function |
-| `unreachable` | `0x0a` | | trap immediately |
+| `nop` | `0x0a` | | no operation |
 | `end` | `0x0f` | | end a block, loop, or if |
 
 Note that there is no explicit `if_else` opcode, as the else clause is encoded with the `else` bytecode.
@@ -367,9 +366,10 @@ out of range, `br_table` branches to the default target.
 | `f32.const` | `0x13` | value : `uint32` | a constant value interpreted as `f32` |
 | `get_local` | `0x14` | local_index : `varuint32` | read a local variable or parameter |
 | `set_local` | `0x15` | local_index : `varuint32` | write a local variable or parameter |
-| `call` | `0x16` | argument_count : `varuint1`, function_index : `varuint32` | call a function by its index |
-| `call_indirect` | `0x17` | argument_count : `varuint1`, type_index : `varuint32` | call a function indirect with an expected signature |
-| `call_import` | `0x18` | argument_count : `varuint1`, import_index : `varuint32` | call an imported function by its index |
+| `select` | `0x16` | | select one of two values based on condition |
+| `call` | `0x17` | argument_count : `varuint1`, function_index : `varuint32` | call a function by its index |
+| `call_indirect` | `0x18` | argument_count : `varuint1`, type_index : `varuint32` | call a function indirect with an expected signature |
+| `call_import` | `0x19` | argument_count : `varuint1`, import_index : `varuint32` | call an imported function by its index |
 
 The counts following the different call opcodes specify the number of preceding operands taken as arguments.