TYPO3 Core

I see... This is because the position of the header can be different, depending on the chosen options.

In that case, why not to conditionally choose the template, depending on the gallery position:

<f:layout name="{f:if(condition:'{gallery.position.noWrap} == 1', then:'ContentFooter', else:'HeaderContentFooter')}" />

The reason behind is that if I modify the layout (to add a frame around the elements, for example), it will also apply to Textmedia elements. Otherwise, I have to modify both the layouts and the Textmedia template.

you can change Textmedia.html to:

<f:layout name="ContentFooter"/>

<f:section name="content">
    <f:if condition="{gallery.position.noWrap} != 1">
        <f:render partial="Header" arguments="{_all}" />
    </f:if>

    <div class="ce-textpic ce-{gallery.position.horizontal} ce-{gallery.position.vertical}{f:if(condition: gallery.position.noWrap, then: ' ce-nowrap')}">
        <f:if condition="{gallery.position.vertical} != 'below'">
            <f:render partial="MediaGallery" arguments="{_all}" />
        </f:if>

        <f:if condition="{data.bodytext}">
            <f:then>
                <div class="ce-bodytext">
                    <f:if condition="{gallery.position.noWrap}">
                        <f:render partial="Header" arguments="{_all}" />
                    </f:if>
                    <f:format.html>{data.bodytext}</f:format.html>
                </div>
            </f:then>
            <f:else>
                <f:if condition="{gallery.position.noWrap}">
                    <f:if condition="{data.header}">
                        <div class="ce-bodytext">
                            <f:render partial="Header" arguments="{_all}" />
                        </div>
                    </f:if>
                </f:if>
            </f:else>
        </f:if>

        <f:if condition="{gallery.position.vertical} == 'below'">
            <f:render partial="MediaGallery" arguments="{_all}" />
        </f:if>
    </div>

</f:section>

and add in the three Layoutfiles

<div id="c{data.uid}" {f:if(condition: data.layout, then: ' class="celayout-{data.layout}"')}>

to use the Layout field.

This changes would it make much easier to add custom Layouts with only change layoutRootPaths.

Would be nice to see it in next Version.

Patch set 66 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 67 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 68 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 69 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 70 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 71 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 72 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 73 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 74 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 75 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 76 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 77 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 78 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 79 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 80 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 81 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 82 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 85 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065

Patch set 86 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51065