Should a tag be singular or plural?

Question

Examples:

• [career] or [careers]
• [design-pattern] or [design-patterns]
• [best-practice] or [best-practices]

Answer 1

Having thought on this I think it's better to have plural tags...

An example with [design-pattern] and [design-patterns].

There might be a question regarding a single design pattern,
but there might also be one regarding multiple design patterns.

Both tags fit well for the first question about a single pattern,
however [design-pattern] doesn't math for the second question about multiple design patterns.

Another reason for plural tags is that a tag lists questions about design patterns, not design pattern.

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However, there are exceptions to this proposed rule:

• Words that shouldn't be plural,
  it's unlikely that a question will be about [careers] so it should be [career].