Fix wrong id fragment

act-rules-format/act-rules-format.bs

@@ -592,7 +592,7 @@ Background (optional) {#background}
 An ACT Rule <em class="rfc2119">may</em> contain information about the background for the development of the rule, or references to relevant reading. The background information is optional, but whenever it is included in the rule, the relationship to the relevant reading can be specified. Examples of relevant background references for a rule for a [Web Content Accessibility Guidelines](https://www.w3.org/WAI/standards-guidelines/wcag/) [[WCAG]] success criterion could be [WCAG 2.1 Understanding documents](https://www.w3.org/WAI/WCAG21/Understanding/), [WCAG 2.1 Techniques](https://www.w3.org/WAI/WCAG21/Techniques/), or [WAI-ARIA 1.1](https://www.w3.org/TR/wai-aria/), CSS [[css-2018]], or HTML [[HTML]] specifications.
 
 
-Implementations (optional) {#implementation}
+Implementations (optional) {#implementations}
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 An ACT Rule <em class="rfc2119">may</em> contain a list of [=implementations=], where each [=implementation=] has one or more [=checks=] that are consistent or partially consistent with that rule. An implementation is an accessibility test methodology or test tool that uses [=checks=] to compute [=outcomes=] indicating whether an [=accessibility requirement=] could be satisfied. These checks can be fully automated, completely manual, or some combination of the two.