The labelChange event in LabelElement is documented[1] as having a parameter, @param {string} value.
However, the two places that trigger the event do so without any parameters[2][3], just this.emit( 'labelChange' );.
Either the parameter should be added, or the documentation corrected.
[1] https://gerrit.wikimedia.org/g/oojs/ui/+/9cbee0a5b5132a8ea0388a058002c23ee01de404/src/mixins/LabelElement.js#44
[2] https://gerrit.wikimedia.org/g/oojs/ui/+/9cbee0a5b5132a8ea0388a058002c23ee01de404/src/mixins/LabelElement.js#177
[3] https://gerrit.wikimedia.org/g/oojs/ui/+/9cbee0a5b5132a8ea0388a058002c23ee01de404/src/mixins/LabelElement.js#197