Why does chrome devtools show more than 6 simultaneous ajax requests?

Question

According to this and a dozen different places chrome and most browsers limit simultaneous http requests to six per domain.

So what exactly am I seeing here?

Isn't that eighteen simultaneous ajax requests?

Here is a sampling of the timing details:

The first request:

The eighth request:

All the requests I've looked at reflect something similar.

What's going on?!

Answer 1

The bar for a request on the timeline starts when the request was enqueued, not when it was sent. If you inspect the timing for one of the later requests (by clicking the name and then the Timing tab) you will probably see that it was Blocking for some amount of time before it was Sending.

code

Here is a fiddle demonstrating this. The requests are sent in batches of six:

... and the later requests show a Blocking time before they are sent: