Anything which has some value in proving a fact in issue generally should be admitted unless there is some specific reason for not admitting it. The rules have as their basic objective the ensuring that the truth is ascertained. But the rules serve other purposes. The rules restricting introduction of irrelevant evidence are designed to prevent unnecessary waste of time. Many rules exclude evidence to avoid undue prejudice to the parties and some evidence is restricted because of other important policies, such as protecting confidential communications.
Foundation refers to the factual basis or existence of circumstances supporting introduction.
For example, the foundation for admissibility of real evidence includes a reasonable basis for concluding that the object is what it purports to be. Reasons for not admitting what would otherwise be admissible evidence include undue prejudice, public policy, privilege, or violation of constitutional rights. See your web browser documentation or online Help, as this procedure may vary with different browsers.