Relevance of facts: background and explanatory facts are admissible when necessary to explain, identify, or contextualize an issue. Section 7 treats as relevant facts those necessary to explain or introduce a fact in issue, to support or rebut inferences, to establish identity of persons or things when material, to fix time or place of a fact in issue, or to show relations among parties to the transaction; extraneous particulars are excluded unless necessary for those purposes.