Problem of using <iframe> in template

I have a field called back which contains HTML.

This works:


This also works (displays “hello” in the iframe):

<iframe srcdoc="<html><body><head><style>some styles</style></head><body>hello</body></html>"></iframe>

However, putting {{back}} in the iframe does not work (blank inside iframe).

<iframe srcdoc="<html><body><head><style>some styles</style></head><body>{{back}}</body></html>"></iframe>

I want to do this because I have multiple fields, each is a piece of HTML with independent, incompatible CSS styles, so I have to display them independently, in separate iframes