diff --git a/css-image-animation-1/Overview.bs b/css-image-animation-1/Overview.bs
index bdca19fb90bc..ae3bad1b7829 100644
--- a/css-image-animation-1/Overview.bs
+++ b/css-image-animation-1/Overview.bs
@@ -132,7 +132,7 @@ Controlling Image Animations: the 'image-animation' property {#image-animation}
Like ''normal'',
the animation of [=animated images=] is run normally,
- as determined by the image format and the host language,
+ as determined by the image format and the host language.
However,
animation timelines are scoped per element:
@@ -141,8 +141,19 @@ Controlling Image Animations: the 'image-animation' property {#image-animation}
the same image data,
and with an 'image-animation' computed value of ''running''
must be rendered synchronized to the same timeline as a group,
- distinct from the timeline of images in other elements,
- with the timeline starting at the time of the least recent addition to the group.
+ distinct from the timeline of images in other elements.
+
+ If images are added to the element while the computed value is ''running'',
+ the timeline starts at the time of the least recent addition to the group.
+
+ If the element is created or made visible after having previously been set to ''display: none'',
+ with images already added and with 'image-animation' already set to ''running'',
+ the timeline starts when the element is included in the layout.
+
+ If this property is switched to ''running'' from another value,
+ the beginnig of this timeline is set
+ so that the animation continues from the state that was displayed
+ at the timem of the switch.