Region-break flow reorder (solution to Head of Line blocking)

When you have a content flow, and regions accross which the content is divided, you inevitably face one difficulty: some elements are too big to fit in the current region, causing a region break, but they are also big enough to make the wasted space important enough for you to want to reclaim it: you would like to “smartly” reorder the content of your flow to avoid HoL blocking. This issue arise a lot with images, for example.

Flow document vs Paged document :

   

Reclaming the lost space could be very nice, especially if the exact location of the image doesn’t matter in your context. Here’s what it could look like :



Sometimes, you may also want to print a replacement content in case of reorder (for exemple a box saying the figure has been moved to next page) :



Here’s an first-attemp proposal to solve the problem :

    figure {
        flow-reorder: allow;
    }
    
    figure::flow-placeholder {
        diplay: block; text-align: center; 
        color: gray; content: ‘See next page for illustration’;
    }

Something maybe interesting would be to make it possible to prohibit cross-chapter reordering (ie: an H1 would never be allowed to be put before any item whose flow reorder is scoped to ‘chapter’).

    figure {
        flow-reorder: allow inside ‘chapter’;
    }

    h1 {
        flow-flush-before: ‘chapter’;
    }
    
Maybe people working at Adobe have a better vision on how to solve this problem, I guess it’s quite common in real life.
François