Add Module.customSections

BinaryEncoding.md

@@ -177,11 +177,11 @@ The module starts with a preamble of two fields:
 | version | `uint32` | Version number, currently 0xd. The version for MVP will be reset to 1. |
 
 The module preamble is followed by a sequence of sections.
-Each section is identified by a 1-byte *section code* that encodes either a known section or a user-defined section.
+Each section is identified by a 1-byte *section code* that encodes either a known section or a custom section.
 The section length and payload data then follow.
-Known sections have non-zero ids, while unknown sections have a `0` id followed by an identifying string as
+Known sections have non-zero ids, while custom sections have a `0` id followed by an identifying string as
 part of the payload.
-Unknown sections are ignored by the WebAssembly implementation, and thus validation errors within them do not
+Custom sections are ignored by the WebAssembly implementation, and thus validation errors within them do not
 invalidate a module.
 
 | Field | Type | Description |
@@ -193,7 +193,7 @@ invalidate a module.
 | payload_data  | `bytes` | content of this section, of length `payload_len - sizeof(name) - sizeof(name_len)` |
 
 Each known section is optional and may appear at most once.
-Unknown sections all have the same `id`, and can be named non-uniquely (all bytes composing their names can be identical).
+Custom sections all have the same `id`, and can be named non-uniquely (all bytes composing their names can be identical).
 Known sections from this list may not appear out of order.
 The content of each section is encoded in its `payload_data`.
 
@@ -413,11 +413,11 @@ a `data_segment` is:
 
 ### Name section
 
-User-defined section string: `"name"`
+Custom section `name` field: `"name"`
 
-The names section does not change execution semantics, and thus is not allocated a section code.
-It is encoded as an unknown section (id `0`) followed by the identification string `"name"`.
-Like all unknown sections, a validation error in this section does not cause validation of the module to fail.
+The names section is a [custom section](#high-level-structure). 
+It is therefore encoded with id `0` followed by the name string `"name"`.
+Like all custom sections, a validation error in this section does not cause validation of the module to fail.
 The name section may appear only once, and only after the [Data section](#Data-section).
 The expectation is that, when a binary WebAssembly module is viewed in a browser or other development
 environment, the names in this section will be used as the names of functions

JS.md

@@ -174,7 +174,7 @@ The `exports` function has the signature:
 Array exports(moduleObject)
 ```
 
-If `moduleObject` is not a `WebAssembly.Module` instance, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+If `moduleObject` is not a `WebAssembly.Module`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
 is thrown.
 
 This function returns an `Array` produced by mapping each
@@ -193,7 +193,7 @@ The `imports` function has the signature:
 Array imports(moduleObject)
 ```
 
-If `moduleObject` is not a `WebAssembly.Module` instance, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+If `moduleObject` is not a `WebAssembly.Module`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
 is thrown.
 
 This function returns an `Array` produced by mapping each
@@ -205,6 +205,25 @@ to the Object `{ module: String(i.module_name), name: String(i.item_name), kind:
 
 Note: other fields like `signature` may be added in the future.
 
+### `WebAssembly.Module.customSections`
+
+The `customSections` function has the signature:
+
+```
+Array customSections(moduleObject, sectionName)
+```
+
+If `moduleObject` is not a `WebAssembly.Module`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+is thrown.
+
+Let `sectionNameString` be the result of [`ToString`](https://tc39.github.io/ecma262/#sec-tostring)(`sectionName`).
+
+This function returns an `Array` produced by mapping each
+[custom section](BinaryEncoding.md#high-level-structure) (i.e., section with
+`id` 0) whose `name` field ([decoded as UTF-8](Web.md#names)) is equal to
+`sectionNameString` to an `ArrayBuffer` containing a copy of the section's
+`payload_data`. (Note: `payload_data` does not include `name` or `name_len`.)
+
 ### Structured Clone of a `WebAssembly.Module`
 
 A `WebAssembly.Module` is a
@@ -248,7 +267,7 @@ If the NewTarget is `undefined`, a [`TypeError`](https://tc39.github.io/ecma262/
 exception is thrown (i.e., this
 constructor cannot be called as a function without `new`).
 
-If `moduleObject` is not a `WebAssembly.Module` instance, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+If `moduleObject` is not a `WebAssembly.Module`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
 is thrown.
 
 Let `module` be the [`Ast.module`](https://github.com/WebAssembly/spec/blob/master/interpreter/spec/ast.ml#L176)