The File Load Progress Event.
This event is dispatched by the Loader Plugin during the load of a file, if the browser receives a DOM ProgressEvent and
lengthComputable event property is true. Depending on the size of the file and browser in use, this may, or may not happen.
Listen to it from a Scene using:
A reference to the File which errored during load.
A value between 0 and 1 indicating how 'complete' this file is.