https://drafts.csswg.org/css-inline/#initial-letter-floats needs more details.

One user of the dropcap.js polyfill has run into a problem where the float simulation of a dropcap interacts badly with multiple same-side floats:

adobe-webplatform/dropcap.js#21

It would be good if we could define initial-letter in such a way that the floated widgets laid out as if the initial-letter did not exist, and the initial-letter would be placed at the top of the in-flow content without reference to the floats or any float clearing.