Several of the more popular tags currently have tag wiki excerpts which I don't find particularly helpful:

  • Tag: X
  • Tag wiki excerpt: Questions related to X.

Should tag wiki excerpts provide a brief description of the subject, or should they (as they seem currently to do) state the (obvious?) fact that questions tagged with the tag have to do with the subject indicated by the tag?

Many tags seem to provide brief descriptions, but many also seem to fall into the category I'm talking about. Would it be better to change these, or not?


3 Answers 3


About both. The purpose of a tag wiki excerpt is to guide people when they are deciding how to tag a question.

If the meaning of the tag is not generally known to anyone who would ask a question in that field, then the excerpt should explain it. For example, does not need a definition, but does. The excerpt doesn't need to have a correct and complete definition, it's enough to give the context.

The excerpt should concentrate on the usage of the tag on the site. If the word has other meanings that are not applicable to computer science, this is irrelevant (unless there is a popular misconception to dispel). If the way the tag name is interpreted on the site is not the way every reasonable computer scientist would understand it, then the excerpt should contain enough guidance to understand what the tag means here.

If there is a risk of confusion between several tags, or if there are many off-topic questions in the tag, then the excerpt may need to mention what questions should not have this tag, and possibly where to ask the question instead. This is fairly rare; related tags and sites are usually only mentioned in the tag wiki.

The official guidance on tag wiki excerpts is in the blog post Improved tagging. For tag wikis in general, read Redesigned tags page.


I browsed the list of tags and found lots of bad descriptions. Take the one for , for instance:

state machines with stacks, capable of accepting the set of context-free languages.

[empty description]

This is my take on it:

Questions about state machines with a single stack for memory. They characterize the class of context-free languages.

The best category tag to use with this one is usually .

Except when conversion from or to automata is concerned, do not use when the question is about or properties of that do not relate to automata!

If you are unsure whether your question is about pushdown automata, you may want to check other questions or the Wikipedia page.

Do not use this tag for automata with more than one stack; tag those and .

  1. I improved the excerpt to talk about questions, not the subject matter at hand.
  2. The longer description focuses on how to use the tag on the site.
  3. For a more detailed take on the subject matter, I simply link to a more elaborate resource; no need to reproduce here.

When creating, improving or reviewing tag wikis, please make sure to give guidance for what and how to use the tag. There is usually no need to give a detailed treatise on the subject matter; link one if you think it is necessary and/or interesting.

Note: Make sure you are describing how the tag is actually used, not how you understand the name. Browse the list of associated questions (fixing obvious mistaggings if need be!) to check.

  • $\begingroup$ I prefered the previous excerpt. What's bad about it? “Questions about” is empty verbiage and should not be used in excerpts where length is at a premium. $\endgroup$ Commented Jan 27, 2016 at 15:32
  • $\begingroup$ @Gilles The previous excerpt does not explain well what PDA are. The "questions about" can be dropped, but I think it's nice to have there. Too many people are tagging "words from the syllabus". $\endgroup$
    – Raphael
    Commented Jan 27, 2016 at 16:49

I think some of those you are referring to are written by me and are area tags and that is the reason for the generality of their excerpt. The previous ones were not general enough.

If you have better descriptions than the current ones that still capture the generality of these areas then post them below and we can discuss them.

One possible idea is to add something similar to the descriptions on arXiv (or ACM CCS), e.g. for we can write an excerpt like:

models of computation, complexity classes, structural complexity, complexity tradeoffs, upper and lower bounds, ...

ps: generally the area tags are familiar to most experts in CS, so not sure being how important is their wiki excerpts as long as they are not misleading and too restrictive.

  • $\begingroup$ I wouldn't say their excerpt is too general... I mean, it says nothing about the subject of the tag at all. I think any description of complexity-theory would be better than saying "questions about complexity theory"... I'm not an expert in complexity theory, and therefore not a great person to suggest a tag... but that definitely doesn't mean that we shouldn't try to do better. I'm not worried about experts being unfamiliar with a tag... that's not who the excerpts are for, right? $\endgroup$
    – Patrick87
    Commented Apr 25, 2012 at 20:39
  • $\begingroup$ I mean, what about something like "theory concerning resources required by computational processes"? It's not great, probably not as general as it should be, but I feel like something in that spirit is what we should be shooting for. There's no need to provide an excerpt like the one you suggest, which seems to begin listing subfields in minute detail. $\endgroup$
    – Patrick87
    Commented Apr 25, 2012 at 20:42
  • $\begingroup$ @Patrick87, I agree they can be improved. At the time I was writing the tag wikis didn't find something good, I mostly focused on their content. You are right that having better excerpts can help users and your point is valid. I will try to think about better excerpts. As I said one idea could be listing some topics in that area as I did for complexity theory above. But it would help to see if there is a better suggestion. $\endgroup$
    – Kaveh
    Commented Apr 25, 2012 at 20:47
  • 1
    $\begingroup$ I remember somebody (Gilles?) saying that tag excerpts should not attempt to define or explain the field they represent, but rather give a quick guideline on which questions should be tagged with it (and for standard, broad areas that probably means stating the obvious). For details, we have the full wiki. $\endgroup$
    – Raphael
    Commented Apr 26, 2012 at 7:00

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