[turtledragonfly]

Is there allowance for file formats whose contents are dynamic, based on the values present in other parts of the file?

For instance "if value at offset X is 123, then treat this other block of data as format ABC, otherwise treat it as as DEF". Obviously can get complex. The Adobe PSD format does horrible things like this all over the place (:

[marlin]

Yes, see the "if statements" section in the (very terse) documentation https://github.com/martinlindhe/feng/blob/main/TEMPLATE.md#i...

You can see it in use in the PNG format template, here: https://github.com/martinlindhe/feng/blob/main/templates/ima...