Bug 1951011 Comment 1 Edit History

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Original comment by
on 
So I imagine to implement this, we need the iframe element's `effective_zoom` to **establish the default `effective_zoom` for the subdocument's root element** (evenif the subdocument is cross-origin).  Probably this would need to be communicated in the same channel that we communicate the iframe element's `height` and `width`.

Moreover, we need to do it in such a way that it will "stack" with any explicit `zoom` value that's specified on the subdocument's root element, rather than being replaced by such a value.  So e.g. the following data-URI example should show the text at the zoom levels described in the text (most notably at the innermost level, "Text zoomed 4x"):
```
data:text/html,<!DOCTYPE html>
  Text at default zoom level
  <div style="zoom:2">Text zoomed 2x<br>
    <iframe srcdoc="<!DOCTYPE html><style>:root{zoom:2}body{margin:0}</style>Text zoomed 4x"></iframe>
```
Revision 1 by
on 
So I imagine to implement this, we need the iframe element's `effective_zoom` to **establish the default `effective_zoom` for the subdocument's root element** (evenif the subdocument is cross-origin).  Probably this would need to be communicated via the same channel & timing that we communicate the iframe element's computed `height` and `width` (and how we handle dynamic changes to them) to establish the size of the inner document's viewport.

Moreover, we need to do it in such a way that this default `effective_zoom` will "stack" on top of any explicit `zoom` value that's specified on the subdocument's root element, rather than being replaced by such a value.  So e.g. the following data-URI example should show the text at the zoom levels described in the text (most notably at the innermost level, "Text zoomed 4x").  
```
data:text/html,<!DOCTYPE html>
  Text at default zoom level
  <div style="zoom:2">Text zoomed 2x<br>
    <iframe srcdoc="<!DOCTYPE html><style>:root{zoom:2}body{margin:0}</style>Text zoomed 4x"></iframe>
```

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