some clarifying comments

src/Calendar.constraints.js

@@ -1,4 +1,8 @@
 
+/*
+determines if eventInstanceGroup is allowed,
+in relation to other EVENTS and business hours.
+*/
 Calendar.prototype.isEventInstanceGroupAllowed = function(eventInstanceGroup) {
 	var eventDef = eventInstanceGroup.getEventDef();
 	var eventFootprints = this.eventRangesToEventFootprints(eventInstanceGroup.getAllEventRanges());

src/common/Grid.event-interaction.js

@@ -193,12 +193,14 @@ Grid.mixin({
 	},
 
 
+	// is it allowed, in relation to the view's validRange?
 	// NOTE: very similar to isExternalInstanceGroupAllowed
 	isEventInstanceGroupAllowed: function(eventInstanceGroup) {
 		var eventFootprints = this.eventRangesToEventFootprints(eventInstanceGroup.getAllEventRanges());
 		var i;
 
 		for (i = 0; i < eventFootprints.length; i++) {
+			// TODO: just use getAllEventRanges directly
 			if (!this.view.validUnzonedRange.containsRange(eventFootprints[i].componentFootprint.unzonedRange)) {
 				return false;
 			}

src/common/Grid.external-dropping.js

@@ -162,6 +162,9 @@ Grid.mixin({
 
 		for (i = 0; i < eventFootprints.length; i++) {
 			// treat it as a selection
+			// TODO: pass in eventInstanceGroup instead
+			//  because we don't want calendar's constraint system to depend on a component's
+			//  determination of footprints.
 			if (!calendar.isSelectionFootprintAllowed(eventFootprints[i].componentFootprint)) {
 				return false;
 			}

src/common/Grid.js

@@ -285,7 +285,7 @@ var Grid = FC.Grid = ChronoComponent.extend({
 	},
 
 
-	/* Converting eventRange -> eventFootprint -> eventSegs
+	/* Converting eventRange -> eventFootprint
 	------------------------------------------------------------------------------------------------------------------*/
 
 
@@ -322,6 +322,10 @@ var Grid = FC.Grid = ChronoComponent.extend({
 	},
 
 
+	/* Converting componentFootprint/eventFootprint -> segs
+	------------------------------------------------------------------------------------------------------------------*/
+
+
 	eventFootprintsToSegs: function(eventFootprints) {
 		var segs = [];
 		var i;