TYPO3 Core

Depending on the setting of the frame_class field, Fluid Styled Content renders two different variants of ids/anchors.

With a frame it will be

<div id="c{data.uid}" class="frame frame-{data.frame_class} frame-type-{data.CType} frame-layout-{data.layout}{f:if(condition: data.space_before_class, then: ' frame-space-before-{data.space_before_class}')}{f:if(condition: data.space_after_class, then: ' frame-space-after-{data.space_after_class}')}">
    <f:if condition="{data._LOCALIZED_UID}">
        <a id="c{data._LOCALIZED_UID}"></a>
    </f:if>
    ....
</div>

without a frame it will be

<a id="c{data.uid}"></a>
<f:if condition="{data._LOCALIZED_UID}">
    <a id="c{data._LOCALIZED_UID}"></a>
</f:if>

In the first case there will be just one additional <a> Tag, in the second there will be two.
Both of them should be removed as soon as the field sectionIndex ("Show in section menus") is disabled, since otherwise those anchors will break the HTML code by adding unwanted tags.
Currently the switch has no impact and the tags will always be there in CMS 8, 9 and 10.