In section "Processing the image candidates", the srcset spec  says:
"The user agent may at any time run the following algorithm to update an img element's image in order to react to changes in the environment. (User agents are not required to ever run this algorithm.)"
The RICG is wondering why this is not at least a SHOULD or a MUST? Most developers would expect this to work like media queries (i.e., always "responsive" to environmental changes).
Some clarification would be great.
PS: the srcset spec does not yet have a component in Bugzilla. Would be great to be able to file bugs there on this spec.