Previous iframe srcdoc approach completely broke because .replace(/"/g, '"')
mangled the stylesheet <link href="..."> into <link href="...">,
causing browser to treat the entire "file://..." as the attribute
value literal. All CSS failed to load → blank/unstyled preview.
New approach:
- iframe.contentDocument.write() takes raw HTML string, NO escaping needed
- All quotes (double and single) pass through untouched
- stylesheet href attributes remain valid
- body class and html attrs pass through cleanly
- Added initWhenReady() polling to ensure iframe contentDocument is available
before first render (avoids race condition where document.write fires
before iframe is fully initialized)
Verified with headless Chrome render — current/next slides now show correct
colors, fonts, layout matching audience view pixel-for-pixel.
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