More control over server island execution

[psmyrdek]

Summary

Introduce more flexibility around server island loading trigger (i.e. automatic vs depending on visibility, etc.).

Background & Motivation

• When compared to multiple variants of client directives, server islands loading strategy is too rigid. For content-intense pages, there may be some secondary or tertiary elements rendered as server islands that should wait for their turn to be executed.

Goals

• Addressing limited loading strategy when compared to client islands.

Example

Just a few random ideas to kickstart the conversation:

<!-- Default -->
<EpisodesGridAstro server:defer />

<!-- Similar to "lazy" img and iframe -->
<EpisodesGridAstro server:defer="lazy" />

<!-- More explicit  -->
<EpisodesGridAstro server:defer="viewport" />

<!-- Defer until another element is ready?  -->
<EpisodesGridAstro server:defer=".cart" />