There appears to be trend where specifications monkey patch a base specification. A monkey patch being a subtle change to an existing algorithm only observable if you have seen both the new and the base specification. Some examples: Custom Elements attempts to redefine the
eval(). (Using dated TR/ URLs here as an exception so these examples remain useful going forward.)
Apparently it is not clear that this is bad design. We should avoid monkey patching (hereafter patching). It has at least these problems:
img element definition it would not be clear for someone reading the adopting algorithm that adopting is actually more involved.
If you encounter patching, please file a bug. If you are writing a specification and temporarily want to patch a base specification to help implementations along, file a bug on the base specification so the community is informed of what you are trying to do.