diff --git a/README.md b/README.md
index 936c561..0c2dee4 100644
--- a/README.md
+++ b/README.md
@@ -28,6 +28,11 @@ The export is deliberately incomplete. Hidden, collapsed, paginated,
 dynamically unloaded, diff, checks, files-changed, and complete review-thread
 content may be omitted.
 
+Here, visible means CSS-rendered or potentially visible. The extractor excludes
+content hidden by `hidden` or `inert`, `display: none`, hidden or collapsed
+visibility, or zero opacity. It does not guarantee that extracted content is
+inside the viewport, unobscured, or currently on-screen.
+
 ## Install locally
 
 1. Clone or download this repository.
diff --git a/docs/06_mv3_design.md b/docs/06_mv3_design.md
index d1edc9a..16e3a12 100644
--- a/docs/06_mv3_design.md
+++ b/docs/06_mv3_design.md
@@ -50,6 +50,13 @@ files-changed content is outside the completeness claim.
 The extractor uses visible `innerText` for page-derived body and comment
 content. It does not fall back to hidden `textContent`.
 
+In this contract, visible means CSS-rendered or potentially visible. Elements
+hidden by `hidden` or `inert`, `display: none`, hidden or collapsed visibility,
+or zero opacity are excluded. The extractor does not claim that retained
+content is inside the viewport, unobscured, or currently on-screen. Viewport
+clipping, IntersectionObserver-based checks, and occlusion detection remain
+outside the runtime design.
+
 ## Rendering principle
 
 Page-derived content is rendered through `textContent` or form-control