iframeDomainsToRenderAsOverlay

A list of domains. If an iframe's src URL matches any domain in the list, the iframe will be rendered in the top window instead of within the EPUB content document iframe.

This is useful because EPUB content documents are often loaded using blob: URLs, which causes nested iframes to inherit an opaque origin. Some third-party sites (like YouTube) do not support loading inside a blob: origin and require a proper origin to send correct origin headers.

Domains can include wildcards (e.g., *.youtube.com), or * to match any domain. Note that a wildcard pattern like *.youtube.com will also match the base domain youtube.com.

Note that iframes matching these domains will load in the top window overlay, bypassing policyType and whitelistDirectives.