One needs a way to define dynamic properties using matchdom expressions for blocks inside template content.
it concerns block properties, not dom attributes
each "constant" block property should have a corresponding "dynamic" property that will be merged as a matchdom expression, and not checked against a schema.
the dynamic properties are stored inline, as data-$ attributes
the ability to carry inline properties for blocks is missing in pagecut.
One needs a way to define dynamic properties using matchdom expressions for blocks inside template content.
Related to #3