2.1.31 [HTML5:2014] Section 4.7.8 The source element

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.

All document modes (All versions)

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