Why does empty @Html.Sitecore().Placeholder("main") generate <div class="row"></div>?

Question

I am working with SXA 1.8 on Sitecore 9.0 update 2. Since Bootstrap 4 is being selected for the current site, ~/Views/SxaLayout/Bootstrap4Body.cshtml view is being used. This view has such a code:

<main>
    <div id="content" class="@Html.Sxa().GridPlaceholderClasses("main")">
        @Html.Sitecore().Placeholder("main")
    </div>
</main>

(I definitely know that particular view is being used since it hits in debugger), but having no components assigned into itself, it rendered with:

<main>
    <div id="content" class="container">
        <div class="row"></div>
    </div>
</main>

Thus there is a question: where does <div class="row"></div> come from and should not be it empty?

Answer 1

For Bootstrap 3, I think these were hardcoded on the body view, but for Bootstrap 4, on this item - /sitecore/system/Settings/Feature/Experience Accelerator/Bootstrap 4/Bootstrap 4 Grid Definition you should see a section that defines the Placeholder Wrapper tag/class

Answer 2

Firstly, remove this line and reload:

@Html.Sitecore().Placeholder("main")

If the row div is still there, then remove this piece of code:

class="@Html.Sxa().GridPlaceholderClasses("main")"

I'm pretty sure that by doing so you will know exactly where this div row line is coming from.

After that, it's just a matter of troubleshooting your own code and start isolating the possible origins to figure out the exact source of this weird line.