Update API shape to support multiple labels per correction.

Author: QueenieZqq

README.md

@@ -9,7 +9,7 @@ Web applications can also benefit from such proofreading capability. This propos
 
 
 1. Error Correction: Correct input text by the user
-2. Error Labeling: For each correction made to each error in the input text, label the error type (e.g. spelling, punctuation, etc.)
+2. Error Labeling: For each correction made to each error in the input text, label the error type(s) (e.g. spelling, punctuation, etc.)
 3. Error Explanation: Annotates each error with a plain language explanation
 
 Note that Labeling & Explanation are independent features that can be either added or dropped.
@@ -50,7 +50,7 @@ const proofreader = await Proofreader.create({
 const corrections = await proofreader.proofread("I seen him yesterday at the store, and he bought two loafs of bread.");
 ```
 
-`proofread()` corrects the input text and returns a list of corrections made. Additional proofreading features can be configured using includeCorrectionTypes and `includeCorrectionExplanations`. When `includeCorrectionTypes` is set to `true`, `proofread()` will provide an error type label for each correction made to each error. When `includeCorrectionExplanations` is set to `true`, `proofread()` will provide an annotation for each error with a plain language explanation.
+`proofread()` corrects the input text and returns a list of corrections made. Additional proofreading features can be configured using includeCorrectionTypes and `includeCorrectionExplanations`. When `includeCorrectionTypes` is set to `true`, `proofread()` will provide the error type labels associated for each correction made to each error. When `includeCorrectionExplanations` is set to `true`, `proofread()` will provide an annotation for each error with a plain language explanation.
 
 Detailed design for the corrections output is [discussed later](#proofreading-correction-output).
 
@@ -197,7 +197,7 @@ dictionary ProofreadCorrection {
   unsigned long long startIndex;
   unsigned long long endIndex;
   DOMString correction;
-  CorrectionType type; // exists if proofreader.includeCorrectionTypes === true
+  sequence<CorrectionType> type; // exists if proofreader.includeCorrectionTypes === true
   DOMString explanation; // exists if proofreader.includeCorrectionExplanations === true
 }
 
@@ -206,6 +206,14 @@ enum CorrectionType { "spelling", "punctuation", "capitalization", "preposition"
 
 `type` only exists when the proofreader object is configured with `includeCorrectionTypes = true`, while `explanation` only exists when the proofreader object is configured with `includeCorrectionExplanations = true`.
 
+Each correction could be associated with mutliple correction type labels. For example:
+
+```js
+const original_text = "`thatd` a good amt of time!!! !" // `thatd` is the text to be corrected
+const proofread_text = "`That's` a good amount of time!" // `That's` is the corrected text
+```
+where the correction from "thatd" to "That's" contains three types of correction - "Captilization", "Spelling" and "Punctuation". When there's only one label, the sequence will be of size 1.
+
 Not all correction types here will be applicable to all languages, and in the future we might propose more specific correction types. The generic catch-all type, if no more-specific type matches, is `"grammar"`.
 
 To get an error in the input, use `input.substring(startIndex, endIndex)`. Corrections in the `corrections` list will be organized in ascending order based on the `startIndex` of the correction.