It is hard to avoid feeling vulnerable to this invisible enemy who does not play by known or explicit rules.

I.e. can't it simply be isolated from doubt, though not according to any explicit rule?

Typical examples of the less important but explicit rules for a particular game include:

However, our explicit, written rules required us to recommend only 6 to 9 applicants from among the more than 30 we found to be qualified.

In schools and colleges competitive debate often takes the form of a contest with explicit rules.

"Nobody's setting down fairly explicit rules about what the rules of the house are," he said.

Today the government also announced more explicit rules governing the religious activities of foreigners in China.

The standard is based on certain principles rather than explicit rules.

If a conventional game can appear so fragile, how much more so does drama with its less explicit rules.

While there are few explicit rules, officers are supposed to identify themselves as the police and try to bring suspects under control with minimal force.