A function to listen for onChange events and test the input contents
for valid information, such as valid urls with http/https/ftp and if
not present, try and guess if the input url is relative or not, and if
Change state of the plugin to respond to events in the editor.
This is called on meaningful events in the editor, such as change of selection
or caret position (but not simple typing of alphanumeric keys). It gives the
plugin a chance to update the CSS of its button.
For example, the "bold" plugin will highlight/unhighlight the bold button depending on whether the
characters next to the caret are bold or not.
Only makes sense when `useDefaultCommand` is true, as it calls Editor.queryCommandEnabled(`command`).
String like "insertUnorderedList", "outdent", "justifyCenter", etc. that represents an editor command.
Passed to editor.execCommand() if useDefaultCommand is true.