[EME] specification question: key Sytem selection

After reading the specification, I have a question on Key System selection.

If media element’s source attribute has a keySystem attribute then we use this as selected keySystem, this is OK.
If no selected KeySystem, the specification says “jump to Key Presence”

The question is :

At “jump to Key Presence” is a else if of “selected key system”, so here we have no idea about key system,
We may need let app or CDM to analyze the initData to find the KeySystem, but I have not seen any text for
Analyzing initData here, or I miss something?

So where we select the Key System if no selected key system in media element?


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孙扬
华为技术有限公司 Huawei Technologies Co., Ltd.
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