TYPO3 what is the .layout deprecation 7.x to 8.x

I'm updating a project from TYPO3 7.6.32 to ^8. In the deprecation log I can find a lot of entries where the issue is:

29-04-19 12:13: EXT:form: Do not use "layout." anymore. Deprecated since TYPO3 CMS 7, this function will be removed in TYPO3 CMS 8.

Questions:

• what is EXT:form (its not an extension in typo3conf/ext/...)
• what is "layout."
• do anyone have any resources on how to rework that case

if any further information is needed just drop a comment, thanks - any help is much appreciated.

This is probably usage of the FORM content object / content element.

See: https://docs.typo3.org/typo3cms/extensions/core/Changelog/7.5/Deprecation-69401-AdoptFormToSupportTheExtbaseFluidMVCStack.html

You might have the following somewhere:

10 = FORM
10 {
        layout {
                containerWrap = <div><elements /></div>
                elementWrap = <div><element /></div>
        }
}

The "layout" part can be removed completely.

The extension "Form" mentioned is a system extension and located in typo3/sysext/form. The layout part was the configuration older versions used to configure the layout - which is nowadays done with FLUID templates.

The form extension layouts can be customized by configuring your own templates in TypoScript - see https://docs.typo3.org/typo3cms/extensions/form/I/FAQ/Index.html#how-do-i-override-the-frontend-templates