How to insert a block content into Page content property without using Running Headers that redirect the block element ? I mean there is an API to redirect something using flow , but is it possible to avoid redirection entirely by being able to specify the HTML inline ? That might also address the same issue

For example is there any API like ->

@page
{
@top {content : url(header_html);}
}

No, including a URL only works for images and SVG, not HTML.

Thanks I think it's a nice feature to have for people who use Templating languages because we already have means to create an HTML string variable through server side programming and you can just stick it in.However is not yet CSS3 specs