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The original `Background` section

One of the most prominent changes from SPDY to HTTP/2 is the introduction of dependency-based stream prioritization.

SPDY only had weight-based prioritization. In weight-based prioritization, every stream (e.g. file being served) is given a weight, and the value is used by the server to proportionally distribute the bandwidth between the streams.

HTTP/2 introduced a new scheme: dependency-based prioritization in addition to the weight-based approach. By using the added prioritization method, web browsers can advise HTTP/2 servers to send the streams that are depended by other streams before sending the other streams. For example, by using dependency-based prioritization web browsers can request the server to send CSS or JavaScript files before sending HTML or image files.

As of this writing, out of the two popular web browsers that implement HTTP/2, only Firefox uses dependency-based prioritization.

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