A more thorough explanation:

Term: tanquam in libello
Definition: This is a Latin phrase used in law. It means "as if alleged in the libel". A libel is a written statement that accuses someone of something. So, when something is said to be "tanquam in libello", it means that it is being treated as if it was written in the libel, even if it wasn't actually written there.
Example: In a court case, the judge might say that a certain fact is "tanquam in libello", meaning that even though it wasn't specifically written in the libel, it is being treated as if it was. For example, if the libel accuses someone of stealing a car, and the defendant's alibi is that they were at home at the time, the judge might say that the fact that the defendant's car was in the shop at the time is "tanquam in libello", meaning that it is being treated as if it was written in the libel, even though it wasn't.