Turn on Ace HTML worker for syntax errors

app/core/utils.coffee

@@ -297,6 +297,8 @@ module.exports.aceEditModes = aceEditModes =
   java: 'ace/mode/java'
   html: 'ace/mode/html'
 
+# These ACEs are used for displaying code snippets statically, like in SpellPaletteEntryView popovers
+# and have short lifespans
 module.exports.initializeACE = (el, codeLanguage) ->
   contents = $(el).text().trim()
   editor = ace.edit el

app/views/play/level/tome/Problem.coffee

@@ -23,6 +23,7 @@ module.exports = class Problem
       raw: text,
       text: text,
       type: @aetherProblem.level ? 'error'
+      createdBy: 'aether'
 
   buildMarkerRange: ->
     return unless @aetherProblem.range

app/views/play/level/tome/SpellPaletteEntryView.coffee

@@ -53,6 +53,7 @@ module.exports = class SpellPaletteEntryView extends CocoView
       oldEditor.destroy() for oldEditor in @aceEditors
       @aceEditors = []
       aceEditors = @aceEditors
+      # Initialize Ace for each popover code snippet
       popover?.$tip?.find('.docs-ace').each ->
         aceEditor = utils.initializeACE @, codeLanguage
         aceEditors.push aceEditor

app/views/play/level/tome/SpellView.coffee

@@ -21,6 +21,7 @@ module.exports = class SpellView extends CocoView
   controlsEnabled: true
   eventsSuppressed: true
   writable: true
+  languagesThatUseWorkers: ['html']
 
   keyBindings:
     'default': null
@@ -78,6 +79,7 @@ module.exports = class SpellView extends CocoView
     @lockDefaultCode()
     _.defer @onAllLoaded  # Needs to happen after the code generating this view is complete
 
+  # This ACE is used for the code editor, and is only instantiated once per level.
   createACE: ->
     # Test themes and settings here: http://ace.ajax.org/build/kitchen-sink.html
     aceConfig = me.get('aceConfig') ? {}
@@ -85,7 +87,7 @@ module.exports = class SpellView extends CocoView
     @ace = ace.edit @$el.find('.ace')[0]
     @aceSession = @ace.getSession()
     @aceDoc = @aceSession.getDocument()
-    @aceSession.setUseWorker false
+    @aceSession.setUseWorker @spell.language in @languagesThatUseWorkers
     @aceSession.setMode utils.aceEditModes[@spell.language]
     @aceSession.setWrapLimitRange null
     @aceSession.setUseWrapMode true
@@ -789,10 +791,12 @@ module.exports = class SpellView extends CocoView
       else
         finishUpdatingAether(aether)
 
+  # Clear annotations and highlights generated by Aether, but not by the ACE worker
   clearAetherDisplay: ->
     problem.destroy() for problem in @problems
     @problems = []
-    @aceSession.setAnnotations []
+    nonAetherAnnotations = _.reject @aceSession.getAnnotations(), (annotation) -> annotation.createdBy is 'aether'
+    @aceSession.setAnnotations nonAetherAnnotations
     @highlightCurrentLine {}  # This'll remove all highlights
 
   displayAether: (aether, isCast=false) ->
@@ -800,7 +804,7 @@ module.exports = class SpellView extends CocoView
     isCast = isCast or not _.isEmpty(aether.metrics) or _.some aether.getAllProblems(), {type: 'runtime'}
     problem.destroy() for problem in @problems  # Just in case another problem was added since clearAetherDisplay() ran.
     @problems = []
-    annotations = []
+    annotations = @aceSession.getAnnotations()
     seenProblemKeys = {}
     for aetherProblem, problemIndex in aether.getAllProblems()
       continue if key = aetherProblem.userInfo?.key and key of seenProblemKeys