This minor release is focused on improvements to the eye tracking features added in version 6.3.0.

New Features

We have forked WebGazer to make some minor changes to improve compatibility with jsPsych. These changes allow jsPsych to sample eye movements at a faster rate without disrupting jsPsych's display timing. Thanks to @moltaire for identifying this issue (#1700).
WebGazer no longer initializes automatically when the page loads. Instead, the webgazer-init-camera plugin will initialize WebGazer and ask for camera access permissions. Added an auto_initialize parameter to the WebGazer extension to allow users to initialize on page load if desired.
The sampling interval can be set in the WebGazer extension. By default the extension aims for 30Hz. Faster intervals are probably not possible until browsers provide better interfaces to synchronize processing with video feeds.
Improved the timing measurements reported by WebGazer by ~30 milliseconds. Timing is now based on an estimate of when the video frame was recorded, instead of when WebGazer finished computational work on the video frame.
jsPsych.pluginAPI.compareKeys can now handle null values: it will return true if both key arguments are null, and return false if one key is null and the other is a key code or key character. This means that this function can be used to check for a correct non-response. (#1577)

Changes

Minor formatting and text updates to the webgazer-init-camera plugin to center the camera view.
The webgazer-validate plugin now records the coordinates of the validation points.
The webgazer-init-camera plugin now records the load time for WebGazer to initialize.
Added a point_size parameter to calibration and validation plugins, and set the default to a larger value.

Fixed an issue where webgazer_targets did not record the bounding box of content on the screen if the content was loaded after the trial began.
Fixed problem with the minimum_valid_rt parameter in jsPsych.init not working when the WebAudio clock is used to measure keyboard RTs (i.e. rt_method: 'audio' in jsPsych.pluginAPI.getKeyboardResponse). Thanks @kinleyid! (#1675)
Fixed various documentation errors and formatting problems. (#1642, #1641, #1594)