¶21 Wisconsin Stat. § 901.03(4) (2003-04) recognizes the plain error doctrine.  The plain error doctrine allows appellate courts to review errors that were otherwise waived by a party’s failure to object. State v. Mayo, 2007 WI 78, ¶29, 301 Wis. 2d 642, 734 N.W.2d 115. See also 7 Daniel D. Blinka, Wisconsin Evidence § 103.7 (2d ed. 2001). Plain error is “‘error so fundamental that a new trial or other relief must be granted even though the action was not objected to at the time.'” State v. Sonnenberg, 117 Wis. 2d 159, 177, 344 N.W.2d 95 (1984) (citation omitted). The error, however, must be “obvious and substantial.” Id. Courts should use the plain error doctrine sparingly. Id. For example, “‘where a basic constitutional right has not been extended to the accused,'” the plain error doctrine should be utilized. Id. (citing Virgil v. State, 84 Wis. 2d 166, 195, 267 N.W.2d 852 (1978) (Beilfuss, C.J., concurring); ” Wisconsin courts have consistently used this constitutional error standard in determining whether to invoke the plain error rule.” State v. King, 205 Wis. 2d 81, 91, 555 N.W.2d 189 (Ct. App. 1996) (citing to a number of Wisconsin cases applying the plain error doctrine).¶22 However, “‘the existence of plain error will turn on the facts of the particular case.'” Mayo, 301 Wis. 2d 642, ¶29 (citing Virgil, 84 Wis. 2d at 190-91). …
¶23 If the defendant shows that the unobjected to error is fundamental, obvious, and substantial, the burden then shifts to the State to show the error was harmless.  Id. (citing King, 205 Wis. 2d at 93). …
 “It is also consistent with federal case law for us to use a harmless error analysis in determining whether to invoke the plain error doctrine.” State v. King, 205 Wis. 2d 81, 92, 555 N.W.2d 189 (Ct. App. 1996). See also United States v. Olano, 507 U.S. 725, 734 (1993). However, unlike the state of Wisconsin where the State holds the burden, in the federal system the burden is on the defendant to show that the error was harmless. King, 205 Wis. 2d at 93. The concurrence advocates for stating the specific language that federal courts use in their plain error doctrine analysis. Instead, the majority decision today incorporates existing Wisconsin case law on that issue in order to clarify Wisconsin’s plain error doctrine. See ¶¶21 and 22 of this opinion. While the concurrence questions what would qualify as fundamental and substantial error under the majority’s test, the federal doctrine, as espoused by the concurrence, raises the same question. The concurrence also asks whether a fundamental and substantial error can be harmless. Under our analysis, any error that satisfies the first prong of our plain error doctrine, i.e., any error that is fundamental, obvious, and substantial, must then undergo the second prong of whether that error is nonetheless harmless. Today we find that the errors constitute plain error. In this case, we are not presented with facts that satisfy the first prong but are harmless under the second prong. In a future case, however, an error may satisfy the first prong but nonetheless be deemed harmless under the second prong’s seven factor test, and thus, the error would not constitute plain error.
“… in the federal system the burden is on the defendant to show that the error was harmless.” Typo, obviously: the burden there is to show the error was prejudicial. The majority appears committed to a two-part plain error analysis: “fundamental,” etc., error; and if so, harmlessness nonetheless. As the court also suggests, plain error is generally limited to constitutional error, as in this case (¶33). Note, as well, that the trial found that the absence of objection was based on counsel’s sound strategy, ¶¶1, 7, 17—the supreme court nonetheless engages in plain error analysis (and for that matter grants relief) without so much as factoring this into the result. It’s hard to see this as anything other than dismissal of the relevance of any strategic basis for lack of objection, at least for purposes of plain error analysis. Perhaps that follows from the fundamental nature of “plain” error, but the court doesn’t say explicitly that that is so.
The court also enunciates general harmless-error principles:
¶23 … To determine whether an error is harmless, this court inquires whether the State can prove “‘beyond a reasonable doubt that a rational jury would have found the defendant guilty absent the error.'”  Mayo, 301 Wis. 2d 642, ¶47 (citation omitted). This court has identified several factors to assist in determining whether an error is harmless: (1) the frequency of the error; (2) the importance of the erroneously admitted evidence; (3) the presence or absence of evidence corroborating or contradicting the erroneously admitted evidence; (4) whether the erroneously admitted evidence duplicates untainted evidence; (5) the nature of the defense; (6) the nature of the State’s case; and (7) the overall strength of the State’s case. Id., ¶48.  If the State fails to meet its burden of proving that the errors were harmless, then the court may conclude that the errors constitute plain error.