Resetting does reset the lesson, but it doesn’t clear the session cache so correct code is still present in memory (or something to this effect). To truly reset, Reset and Refresh to begin a brand new session with an empty cache. This is how I have come to think of it, anyway.

The first of your examples is “well formed”; the second has a validation error (the semi-colon after the attribute) which may or may not be ignored, even by a validator (have to try it at validator.w3.org); and the third shouldn’t even work, but the browser may ignore the incorrect bits and try to render what it can make sense of: A single cell with red text.

You are wise to experiment and bring this up, since half of learning what we can or should do stems from learning what we cannot or should not do. They are like inverse analogs of each other, so to speak.

As for the SCT, well that’s a beast of many colors and behaviors since nearly every lesson checks for different things relating to the instructions, and not much else. The SCT can let a lot of stuff by if the interpreter doesn’t throw an error, and sometimes even then the SCT will let it pass.

We cannot rely upon the SCT as an authority, for this simple reason. Each lesson checker is written by a human with a particular aim in mind. Things get overlooked. Anything that makes you think or wonder is worth taking a moment out to research and read up on. No detail is too small or insignificant, and every question deserves an answer before moving on so it doesn’t plague us down the road. Find those answers as you go.