StarView's own template representation, rendering to HTML and diffing into element patches. Compiled templates hold a StarView.Template.Program with evaluated values. Hand-built templates hold StarView.Template.Node trees.

A snapshot holds already-evaluated values. Building one runs every chosen expression exactly once. Compiled rendering merges static markup; diff/2 materializes both trees and can cost more than rendering a bounded region. It saves bytes on the wire, not database reads or expression evaluation.

Rendering

Compiled templates have nodes: nil; use nodes/1 to inspect their tree. A template must hold either nodes or a compiled program, never both.

to_html/1 and to_iodata/1 render server-side HTML. Static text and static attribute values are trusted compiler output and emitted verbatim. Dynamic values and attributes are escaped through the public Phoenix.HTML API with HEEx escaping rules, so rendering dynamic content needs :phoenix_html. Templates implement Phoenix.HTML.Safe for serialization by the Phoenix host. The native template tree rejects legacy HEEx values; components and slots used inside ~STAR must also return StarView.Template.

Diffing

diff/2 compares a previous snapshot with the next one and returns either {:ok, patches} or {:reset, reason}. Send each StarView.Template.Patch with StarView.Elements.patch/3; on reset, send the whole region again.

Patches target existing elements by their DOM id. An element is a target only when:

• its id is the element's only id attribute, matches [A-Za-z][A-Za-z0-9_-]* and is unchanged;
• that id appears exactly once in both snapshots;
• its tag, voidness and namespace are unchanged;
• every ancestor has the same structure, branch keys and keyed order.

Any other change bubbles up to the nearest target ancestor. A patched element replaces all of its descendants' patches, so patches never overlap.

Reset reasons:

• :initial - there is no baseline.
• :template_changed - the template fingerprint changed.
• {:unaddressable, reason} - a change has no target ancestor.
• {:duplicate_key, key} and :missing_key - a keyed collection has ambiguous item identity.

Limitations

• Legacy HEEx values are incompatible. Inline ~H sigils fail during compilation; legacy component/slot results fail with a conversion error during evaluation. Convert the page and its called components together.
• Trusted raw HTML remains opaque; ids inside it cannot be checked for duplicates against the template. Keep document-wide ids unique.
• Descendants of svg and math, template, head, raw-text elements, custom elements (such as Rocket hosts), elements marked data-ignore* and nodes with meta[:browser_owned?] are never targets. Changes there patch the nearest ancestor, which keeps the existing server-markup behavior rather than integrating with browser-owned lifecycles.
• Patches always use the :outer mode and the :html namespace.
• Targeting assumes the rendered HTML nests validly, so the browser keeps every element where the template put it.