CKEditor5: How to create model element value from data attribute? - ckeditor

Question

I have legacy html data that I'm trying to edit with CKEditor5. The data format is:
<my-data-element url="https://something.com/more/stuff"></my-data-element>
The desired model format is
<my-model-element>
https://something.com/more/stuff
</my-model-element>
where the url attribute in the data is now the text of the model element. my-model-element is an editable widget so the user can easily modify the existing URL, copy/paste/etc. When the model is convert to data, the text in my_model-element should be converted to the url value for my-data-element. Reading the value of the url attribute is relatively easy, but I can't figure out how to set the text of the my-model-element. While this looks similar to a link, it's not a link. I considered borrowing from the link editing code, but that's a lot of code and this should be a root level object.
For data down casting, extracting the value of the element to set as the url is easy. The code below leaves the text of my-model-element in my-data-element but I can deal with that for now. It also results in my-data-element having the attribute undefined="undefined", for some reason, but I can also live with that.
schema.register( 'my-model-element', {
isObject: true,
allowWhere: '$block',
allowAttributes: ['url'],
allowContentOf: '$block'
} );
conversion.for( 'dataDowncast' ).elementToElement( {
model: 'myElement',
view: ( modelItem, {writer: viewWriter } ) => {
const data = modelItem.getChild(0).data;
const elem = viewWriter.createContainerElement (
'my-data-element', { url: data }
);
return elem;
}
} );
conversion.for( 'dataDowncast' ).attributeToAttribute( {
model: 'url',
// view has to be a function or the url doesn't get updated
view: () => 'url',
});
For up casting I can get the url from my-data-element, but have not been successful setting the text of my-model-element. Instead, the text value of my-model-element remains empty.
conversion.for( 'upcast' ).elementToElement( {
model: ( viewElement, {writer: modelWriter }) => {
// Pulling the URL works
const url = viewElement.getAttribute('url');
// But creating the child of the new element doesn't
const text = modelWriter.createText(`${url} DOESNT WORK`);
const elem = modelWriter.createElement('my-model-element', {}, text);
return elem;
},
view: {
name: 'my-data-element',
}
} );
I've read the majority of the CKEditor5 documentation on up and down casting, and the tutorials on block, inline, and data driven widgets.