Fix invoking wrong function, add comment

Author: BlueWinds

packages/driver/src/cy/commands/commands.ts

@@ -16,7 +16,7 @@ const command = function (ctx, name, ...args) {
 }
 
 export default function (Commands, Cypress, cy) {
-  $Chainer.add('command', function command (chainer, userInvocationStack, args) {
+  $Chainer.add('command', function (chainer, userInvocationStack, args) {
     // `...args` below is the shorthand of `args[0], ...args.slice(1)`
     // TypeScript doesn't allow this.
     // @ts-ignore

packages/driver/src/cypress/chainer.ts

@@ -8,10 +8,17 @@ export class $Chainer {
 
   constructor (specWindow) {
     this.specWindow = specWindow
-    // the id prefix needs to be unique per origin, so there are not
+    // The id prefix needs to be unique per origin, so there are not
     // collisions when chainers created in a secondary origin are passed
     // to the primary origin for the command log, etc.
     this.chainerId = _.uniqueId(`ch-${window.location.origin}-`)
+
+    // firstCall is used to throw a useful error if the user leads off with a
+    // parent command.
+
+    // TODO: Refactor firstCall out of the chainer and into the command function,
+    // since cy.ts already has all the necessary information to throw this error
+    // without an instance variable, in one localized place in the code.
     this.firstCall = true
   }