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type Layout Pattern
name imposter
title imposter
category Overlay / Exception
description Place an overlay region over a parent without changing document order.
aliases
overlay over parent
positioned overlay
modal over card
오버레이
겹쳐 띄우기
primary_spatial_problem Place an overlay region over a parent without changing document order.
secondary_spatial_problems none
layout_axis both
content_shape mixed
responsiveness fixed
constraints Uses only local class hooks and explicit layout constraints.
scroll_ownership No internal scroll container.
source_lineage https://every-layout.dev/layouts/
lifecycle generated
generated_from scripts/generate-patterns.mjs, scripts/pattern-data.mjs

imposter

When To Use

Use this pattern when you need to place an overlay region over a parent without changing document order.

HTML

<section class="imposter_anchor" aria-label="Draft editor">
    <p>Draft body text stays in normal document flow.</p>
    <section class="imposter" aria-label="Modal placement">
        <dialog open>Unsaved changes confirmation</dialog>
    </section>
</section>

CSS

.imposter_anchor {
    position: relative;
}

.imposter {
    display: grid;
    inset: 0;
    place-items: center;
    position: absolute;
    z-index: 1;
}

Core Properties

  • position, display, inset, place-items, z-index define the spatial behavior for this pattern.

Properties That Break The Layout If Removed

  • Removing position, display, inset, place-items, z-index changes the pattern from its documented layout responsibility back toward ordinary flow or an unsafe fixed arrangement.

Constraints And Change Points

  • fixed responsiveness is part of the contract; change sizing values only when the new minimum, maximum, or wrap point is documented with the pattern.
  • Keep the HTML class hooks and CSS selectors in one-to-one agreement.

Scroll Ownership

No internal scroll container.

Accessibility And Source Order Notes

  • Semantic role expectation: Preserve the HTML sample's landmark, list, navigation, form, figure, or article roles; layout classes must not replace semantic elements.
  • DOM order expectation: Keep semantic elements, DOM order, reading order, and focus order independent from the visual placement created by the layout classes.
  • Focus risk: Any interactive descendants follow DOM order; do not use this pattern to create a visual order that keyboard focus cannot follow.
  • Scroll expectation: No internal scroll container.
  • Cognitive risk: Low: the pattern should preserve ordinary reading flow when semantic order is already correct.

Browser And Fallback Notes

The CSS uses modern grid, flex, intrinsic sizing, logical properties, or positioning. If a target browser cannot support a property, fall back to ordinary block flow before adding decorative or script-driven layout behavior.

Composition Notes

Use imposter as the stable pattern root and compose additional layout behavior outside that root unless the child class is part of the documented relationship.

Anti-patterns

  • Do not add color, border, shadow, typography, or animation rules to reusable pattern CSS.
  • Do not use this pattern to repair unclear HTML structure; make the DOM roles legible first.

IA Navigation

Parent: Overlay / Exception patterns in Pattern Categories. Next: Layout Recipes for screen-level composition, or return to the Layout Pattern Catalog when choosing another primitive.