3. Any line starting with digit and .

I took this to mean "Any line starting with a digit that is immediately followed by a period". (And I wouldn't be surprised to find this really should be "starting with digits..." rather than "a digit...")

2. Any line starting with a word

This is the one that always gives me pause. The common assumption seems to be that the definition, regex or otherwise, of a 'word' is perfectly straightforward, but I can see too many variations to be comfortable with this.