Added comments for the priority function

modules/tiles/src/tileset/tile-3d.js

@@ -175,6 +175,11 @@ export default class TileHeader {
   _getPriority() {
     const traverser = this.tileset._traverser;
     const {skipLevelOfDetail} = traverser.options;
+
+    /* Tiles that are outside of the camera's frustum could be skipped if we are in 'ADD' mode
+     * or if we are using 'Skip Traversal' in 'REPLACE' mode.
+     * In 'REPLACE' and 'Base Traversal' mode, all child tiles have to be loaded and displayed,
+     * including ones outide of the camera frustum, so that we can hide the parent tile. */
     const maySkipTile = this.refine === TILE_REFINEMENT.ADD || skipLevelOfDetail;
 
     // Check if any reason to abort
@@ -185,6 +190,7 @@ export default class TileHeader {
       return -1;
     }
 
+    // Based on the priority function `getPriorityReverseScreenSpaceError` in CesiumJS. Scheduling priority is based on the parent's screen space error when possible.
     const parent = this.parent;
     const useParentScreenSpaceError =
       parent && (!maySkipTile || this._screenSpaceError === 0.0 || parent.hasTilesetContent);