The example explains how to write a custom widget for the form editor.
The source code of the example can be found here:
https://github.com/alkacon/opencms-documentation/tree/branch_11_0_x/com.alkacon.opencms.documentation.examples.contenteditor.nativewidget
The figure shows the demo content using the widget. It's used in the upper two editor field sequences. The last sequence shows the default string widget shipped with the core.