2.1.23 [W3C-HTML51] Section 4.7.12 The source element

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V0054: Appending a source element using appendChild does not invoke the resource selection algorithm when the element is appended

The specification states:

 ... The source element
     ...
     If a source element is inserted as a child of a media element that has no src 
     attribute and whose networkState has the value NETWORK_EMPTY, the user agent must 
     invoke the media element's resource selection algorithm.

EdgeHTML Mode

Appending a source element using appendChild does not invoke the resource selection algorithm when the element is appended.