Type in the input field to see the variable $title change.
Hover the mouse to see the title attribute text popup.
Inspect DCE node in dev tools to see `title` attribute updated while typing.
Attributes processing To be available in template, custom-element attributes should be defined by attribute markup as shown above. The value is taken from attribute text content or from select XPath expression
Declared in such way, attributes are exposed via observedAttributes.
The template exposes those attributes as xsl:param which makes the attribute value available as xsl variable (as attribute name prefixed with $).
After transformation the attributes values are read from CE root and copied into DCE component.
The DCE attribute change from outside invokes attributeChangedCallback which triggers DCE re-render.

The value attribute is usual case to be propagated from within of custom-element. See the using custom-element as form input example.

• Design docs