Section 276 of the Criminal Code precludes the admission of evidence that the complainant has engaged in sexual activity other than the sexual activity that forms the subject-matter of the charge.

If the subject-matter of the proposed evidence falls outside the statutory language, the exclusionary terms of the provision do not apply. 

R. v. M.T., 2012 ONCA 511 (CanLII), at para. 31.

Questions that focus on the fact that the complainant has made a previous allegation of sexual assault, rather than the details of the episode, do not trigger the admissibility rules of section 276.

R. v. M.T., 2012 ONCA 511 (CanLII), at para. 34: 
The admissibility rules of s. 276 apply only where the evidence proposed for admission is of extrinsic sexual activity on the part of the complainant. A previous allegation of sexual assault, without more, will fall outside the section.”

R. v. M. (A.G.) (1993), 1993 CanLII 4309 (QC CA).

R. v. Gervais, 1990 CanLII 3701 (QC CA), at para. 60 (per Justice Fish, prior to his appointment to the Supreme Court of Canada):

Evidence that the complainant has made another allegation of sexual assault, does not, without more, comprise evidence that the complainant has engaged in sexual activity within the meaning of section 276.  This remains good law (see above) notwithstanding R. v. Gervais was decided a year before the section 276 provisions, as they then stood, were struck down by the Supreme Court of Canada in R. v. Seaboyer, 1991 CanLII 76 (SCC).  The current version of 276 was enacted in response to Seaboyer.

Where counsel seeks to question a complainant on the fact she/he has made another allegation of sexual assault and proceeds without an application under section 276, the trial judge should vet counsel’s proposed line of questioning to help ensure that it and the answers it may elicit remain outside the ambit of section 276.
And, as is always the case, the evidence must be relevant to a material issue.
Criminal Code.
Evidence of complainant’s sexual activity
276 (1) In proceedings in respect of an offence under section 151, 152, 153, 153.1, 155 or 159, subsection 160(2) or (3) or section 170, 171, 172, 173, 271, 272 or 273, evidence that the complainant has engaged in sexual activity, whether with the accused or with any other person, is not admissible to support an inference that, by reason of the sexual nature of that activity, the complainant
(a) is more likely to have consented to the sexual activity that forms the subject-matter of the charge; or
(b) is less worthy of belief.
(2) In proceedings in respect of an offence referred to in subsection (1), no evidence shall be adduced by or on behalf of the accused that the complainant has engaged in sexual activity other than the sexual activity that forms the subject-matter of the charge, whether with the accused or with any other person, unless the judge, provincial court judge or justice determines, in accordance with the procedures set out in sections 276.1 and 276.2, that the evidence
(a) is of specific instances of sexual activity;
(b) is relevant to an issue at trial; and
(c) has significant probative value that is not substantially outweighed by the danger of prejudice to the proper administration of justice.