Is it not wise to always expect semantically correct mark-up, in my own and others code?

1. Is it bad to be semantic purist all the time, at work? is it not achievable all the time ?

2. when i saw code of any other person/interviewee. I know selection of element for a purpose is most important thing.

   what i should judge person ability from his code; from a good written, managed, optimized css or how he wrote class and id names?

   Or both every time.

Is it bad to be semantic purist all the time, at work? is it not achievable all the time?

Yes. Sometimes the tools doesn't work the way that you would like, and you just have to use something that does work. It's worth a little effort to make the code more semantically correct to make maintenance more effective, but at some point you just can't defend the development cost because the gain in maintenance that it would give is a lot less.

what i should judge person ability from his code; from a good written, managed, optimized css or how he wrote class and id names?

Anyone can have bad habits or incomplete knowledge in some areas. You should rather judge a person on the ability to see the difference between good and bad code when presented with it, and for showing a certain interrest in getting it right.

It depends on what you mean by "semantic purist".

Is his code so bad that you MUST refactor it first before you can do any maintenance on it or even be able to understand what the heck it does? Then it's important.

If the code is not perfect by your standards but udnerstandable, AND can be maintained, AND the person seems receptive to your hints about ways to improve it - especially if those hints are accompanied by explanation of why the improvement makes the code X% more readable/stable/maintainable, it's not THAT important what their level of "purity" is now.

If the person is willing to spend extra week polishing their code to be semantically pure at the cost of shipping late, he's a net loss by a big margin.

To give a specific example for css, if someone will add a class to EVERY element on a page just because it "should be added", bad.

If they indicate that the class needs to be added to places X, Y and Z so that jQuery selectors perform 20% better than alternative solution, VERY GOOD.

Both actually contribute to different abilities. A great abstraction design in Classes and Properties will depict his ability to analyze things where as a well writted managed optimized css expresses that he is himself/herself an organized person. The later property is also very important. Still I will go for the first property if the css is atleast presentable.

Are you in danger of setting up a false alternative? We can either choose class and identifier names carefully or we can write working CSS? Ideally I'd prefer someone who can do both.

What do you deduce about the likely quality of a person's work if their job application has serious misspellings? Like the misspelling the name of the company they are applying to! What do you deduce about a project proposal that mis-states the objectives of the project? A person applying for a SW security job who confuses "authentication" and "authorisation".

In the interview you are trying to determine from a very small sample of information the likely way a person will perform if they come to work for you. We need to factor in many factors such as the effect of interview pressure on some folks performance, and whether they are working in their native language. I don't see any absolute standards here, and no scope for simple either-or questions such as you pose.

Of course we need them to be able to produce code that works, that's the easy bit! Quality of code, and quality of other aspects of work also do matter.