Tolerating Postel’s law
This principle can be contentious. When browsers are lax about what they expect, the system works better but also it encourages laxness on the part of web page writers. The principle of tolerance does not blunt the need for a perfectly clear protocol specification which draws a precise distinction between a conformance and non-conformance. The principle of tolerance is no excuse for a product which contravenes a standard.
I assume the term “product” in the last sentence to include web pages. This is a clear point of view, expressed with much more measure, balance and cogency than what I managed.