Cross-examination--described by Wigmore as "the greatest legal engine ever invented for the discovery of truth" ( People v. Reynolds (1984) 152 Cal. App. 3d 42, 46 199 Cal. Rptr. 379, quoting 5 Wigmore, Evidence (3d ed. 1940) 1367, p. 29; see also Dutton v. Evans (1970) 400 U.S. 74, 89 91 S. Ct. 210, 219-220, 27 L. Ed. 2d 213; Bruton v. United States (1968) 391 U.S. 123, 135-137 88 S. Ct. 1620, 1627-1629, 20 L. Ed. 2d 476)--has two purposes. Its chief purpose is "to test the credibility, knowledge and recollection of the witness. (Sharp v. Hoffman (1889) 79 Cal. 404, 408, 21 P. 846; Razzo v. Varni (1889) 81 Cal. 289, 292, 22 P. 848 'to sift, explain, or modify what has been said on the examination in chief, and to discredit the witness'; Neal v. Neal (1881) 58 Cal. 287, 288 . . .) The other purpose is to elicit additional evidence." (3 Witkin, Cal. Evidence (3d ed. 1986) 1873, p. 1827; see also Priestly v. Superior Court (1958) 50 Cal. 2d 812, 822 330 P.2d 39 (conc. opn. of Carter, J.).) Because it relates to the fundamental fairness of the proceedings, cross-examination is said to represent an "absolute right," not merely a privilege ( People v. Abner (1962) 209 Cal. App. 2d 484, 489 25 Cal. Rptr. 882; People v. Flores (1936) 15 Cal. App. 2d 385, 401 59 P.2d 517), and denial or undue restriction thereof may be reversible error. (People v. Redwine (1958) 166 Cal. App. 2d 371 333 P.2d 188.) This is the view not just of California courts but of the highest court of our land, which has declared: "Cross-examination of a witness is a matter of right. Its permissible purposes, among others, are . . . that facts may be brought out tending to discredit the witness by showing that his testimony in chief was untrue or biased. Counsel often cannot know in advance what pertinent facts may be elicited on cross-examination. for that reason it is necessarily exploratory; and the rule that the examiner must indicate the purpose of his inquiry does not, in general, apply. It is the essence of a fair trial that reasonable latitude be given the cross-examiner, even though he is unable to state to the court what facts a reasonable cross-examination might develop. Prejudice ensues from a denial of the opportunity to place the witness in his proper setting and put the weight of his testimony and his credibility to a test, without which the jury cannot fairly appraise them. To say that prejudice can be established only by showing that the cross-examination, if pursued, would necessarily have brought out facts tending to discredit the testimony in chief, is to deny a substantial right and withdraw one of the safeguards essential to a fair trial. "(Alford v. United States (1930) 282 U.S. 687, 691-692 51 S. Ct. 218, 219, 75 L. Ed. 624; accord, Chambers v. Mississippi (1973) 410 U.S. 284, 295 93 S. Ct. 1038, 1045-1046, 35 L. Ed. 2d 297; Smith v. Illinois (1968) 390 U.S. 129, 131 88 S. Ct. 748, 749, 19 L. Ed. 2d 956; Douglas v. Alabama (1965) 380 U.S. 415, 419-420 85 S. Ct. 1074, 1077-1078, 13 L. Ed. 2d 934.) In short, cross-examination is "an essential and fundamental requirement for the kind of fair trial which is this country's constitutional goal." (Pointer v. Texas (1965) 380 U.S. 400, 405 85 S. Ct. 1065, 1068, 13 L. Ed. 2d 923.)