Context Area

Every ui! { … } block opens with a context header:

use xrune::ui;
fn app(parent_expr: i32) {
ui! {
    :(
        parent: parent_expr
    :)

    placeholder {}
}
}
fn main() {}

:( and :) are literal token pairs. Inside live one or more attributes in the same name: value shape used elsewhere in the DSL. Each attribute sits on its own line.

What parent means

parent is the only required context key. The parser rejects a header without it:

Root node must have a parent

The rune retrieves the parent expression via DsRoot::get_parent(). For DefaultRune this is the value passed to inscribe_root; a real backend typically threads it as the spawn-under / mount-on entity for the rest of the cast.

Other keys are rune-defined

get_context_attrs() returns every attribute the header carried. xrune itself only consumes parent; everything else is yours to interpret:

use xrune::ui;
struct App { world: u32 }
enum Theme { Dark }
fn run(root_entity: i32, app: &mut App) {
ui! {
    :(
        parent: root_entity,
        world: &mut app.world,
        theme: Theme::Dark
    :)
    placeholder {}
}
}
fn main() {}

A rune that doesn’t understand world simply doesn’t read it. There is no compile-time validation that theme is a real symbol — that’s the rune’s job, in inscribe_root or in a sealing pass.

Multi-line layout

The header always spans multiple lines, with each attribute on its own line:

use xrune::ui;
struct App { world: u32 }
enum Theme { Dark }
fn run(root_entity: i32, app: &mut App) {
ui! {
:(
    parent: root_entity
    world: &mut app.world
    theme: Theme::Dark
:)
placeholder {}
}
}
fn main() {}

Putting two or more attributes on the same line raises a parse error:

root header must be multi-line — put each context attr on its own line

Commas between attributes are optional — the shape below is equally valid:

use xrune::ui;
fn run(parent: i32, world: &mut u32) {
ui! {
:(
    parent: parent,
    world: &mut world,
:)
placeholder {}
}
}
fn main() {}

Source-of-truth

DsRoot::parse in crates/xrune_nexus/src/ds_node/ds_root.rs. The behaviour above is exercised by root_header_* tests in crates/xrune_nexus/src/tests.rs.