TYPO3 Core

This is a change of behavior in TypoScript v12.

Given TS:

lib.prototype {
    fields {
        content {
            fields {
                header = TEXT
                header {
                    field = header
                }
            }
        }
    }
}

lib.additionalField {
    fields {
        content {
            fields {
                enlargeImageOnClick = true
            }
        }
    }
}

testElement =< lib.prototype
testElement < lib.additionalField

testElement {
    fields {
        content {
            fields {
                subheader = TEXT
                subheader {
                    field = subheader
                }
            }
        }
    }
}

tt_content.testElement =< lib.prototype
tt_content.testElement < lib.additionalField

tt_content.testElement {
    fields {
        content {
            fields {
                subheader = TEXT
                subheader {
                    field = subheader
                }
            }
        }
    }
}

In v11 it looked like:

In v12 it is:

see missing "=< lib.prototype" in v12.
What is also interesting. Is that neither in v11 nor in v12 there is no "=< lib.prototype" if the testElement is on the root level of TS.