diff --git a/docs/requirements.md b/docs/requirements.md
index bfa289b..a22bd10 100644
--- a/docs/requirements.md
+++ b/docs/requirements.md
@@ -542,8 +542,23 @@ region.
 
 ### 3.6 Export
 
-**FR-EXP-1 — Formats.** Export to JPEG, PNG, TIFF (8 and 16-bit), and AVIF or JPEG XL. Quality,
-chroma subsampling, and bit depth are configurable.
+**FR-EXP-1 — Formats.** Export to JPEG, PNG, and TIFF (8 and 16-bit). Quality, chroma subsampling,
+and bit depth are configurable.
+
+**AVIF and JPEG XL are post-v1** and are not part of this requirement's acceptance. Either may still
+be listed in the settings page before its encoder exists, on one condition: choosing it shall fail
+with a typed error naming the format, never with a file. `every_offered_format_either_encodes_or_explains_itself`
+walks every format the page offers and enforces exactly that, so a format cannot be added to the
+picker and quietly reach an encoder that does not handle it.
+
+*On splitting this requirement.* It read as one undifferentiated list — "JPEG, PNG, TIFF (8 and
+16-bit), and AVIF or JPEG XL" — which left it neither met nor unmet. Three formats, both TIFF
+depths, and the configurability clause are built, encode, embed their profile, and are tested; the
+fourth item is a deliberate deferral, and the encoders for it are the two with the least settled
+library support. Fused into one sentence, the only choices were a tag asserting something untrue or
+no tag at all, and the second is the worse of the two: it would have removed the register's record
+of four-fifths of a requirement that is finished. The deferral is now stated where it can be read as
+a decision rather than inferred from an error variant.
 
 **FR-EXP-2 — Colour space.** Export in a selectable output colour space (sRGB, Display P3,
 Adobe RGB, ProPhoto), with the correct ICC profile embedded.