TYPO3 Core

Here is an example :)

<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<T3DataStructure>
    <meta>
        <langDisable>1</langDisable>
    </meta>
    <sheets>
        <sDEF>
            <ROOT>
                <TCEforms>
                    <sheetTitle>Configuration</sheetTitle>
                </TCEforms>
                <type>array</type>
                <el>
                    <settings.viewDirectory>
                        <TCEforms>
                            <label>RootPath</label>
                            <exclude>1</exclude>
                            <config>
                                <type>input</type>
                            </config>
                        </TCEforms>
                    </settings.viewDirectory>
                </el>
            </ROOT>
        </sDEF>
        <engine_configuration>
            <ROOT>
                <TCEforms>
                    <sheetTitle>LLL:EXT:my_ext/Resources/Private/Language/locallang.xlf:flexforms_tab.engine_configuration</sheetTitle>
                </TCEforms>
                <type>array</type>
                <el>
                    <settings.other_fields>
                        <section>1</section>
                        <type>array</type>
                        <el>
                            <field>
                                <type>array</type>
                                <tx_templavoila>
                                    <title>LLL:EXT:my_ext/Resources/Private/Language/locallang.xlf:flexforms_tab.element</title>
                                </tx_templavoila>
                                <el>
                                    <type_field>
                                        <TCEforms>
                                            <label>Type</label>
                                            <onChange>reload</onChange>
                                            <exclude>1</exclude>
                                            <config>
                                                <type>select</type>
                                                <items type="array">
                                                    <numIndex index="10" type="array">
                                                        <numIndex index="0">Parent categories</numIndex>
                                                        <numIndex index="1">categories_parent</numIndex>
                                                    </numIndex>
                                                    <numIndex index="12" type="array">
                                                        <numIndex index="0">Multidatepicker</numIndex>
                                                        <numIndex index="1">multidatepicker</numIndex>
                                                    </numIndex>
                                                </items>
                                                <minitems>0</minitems>
                                                <maxitems>1</maxitems>
                                                <size>1</size>
                                            </config>
                                        </TCEforms>
                                    </type_field>
                                    <default_value>
                                        <TCEforms>
                                            <label>Values</label>
                                            <exclude>1</exclude>
                                            <config>
                                                <type>input</type>
                                            </config>
                                            <displayCond>
                                                <OR>
                                                    <numIndex index="1">FIELD:type_field:!=:multidatepicker</numIndex>
                                                </OR>
                                            </displayCond>
                                        </TCEforms>
                                    </default_value>
                                    <field_select_categories_parent>
                                        <TCEforms>
                                            <label>Select</label>
                                            <exclude>1</exclude>
                                            <config>
                                                <type>select</type>
                                                <renderMode>tree</renderMode>
                                                <treeConfig>
                                                    <parentField>parent</parentField>
                                                    <appearance>
                                                        <collapseAll>TRUE</collapseAll>
                                                        <showHeader>TRUE</showHeader>
                                                    </appearance>
                                                </treeConfig>
                                                <foreign_table>sys_category</foreign_table>
                                                <size>10</size>
                                                <autoSizeMax>20</autoSizeMax>
                                                <minitems>0</minitems>
                                                <maxitems>20</maxitems>
                                            </config>
                                        </TCEforms>
                                    </field_select_categories_parent>
                                </el>
                            </field>
                        </el>
                    </settings.other_fields>
                </el>
            </ROOT>
        </engine_configuration>
    </sheets>
</T3DataStructure>

Have you some news ?

can you try if it's still an issue with newest TYPO3 8.3?

Patch set 26 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 27 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 28 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 29 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 30 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 31 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 32 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 33 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 34 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 35 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 36 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 37 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 38 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 39 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 40 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 41 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 42 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 43 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 44 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 45 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 46 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 47 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879

Patch set 48 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/50879