Allow removing elements from a list of values in a record

[MrTango]

On install we can add values as follows:

<records interface="Products.CMFPlone.interfaces.controlpanel.IFilterSchema" prefix="plone">
    <value key="custom_attributes" purge="false">
      <element>slot</element>
    </value>
</records>

with purge="false" this will only add values.

We need a way to remove elements (values) from a list.
Somthing like this:

 <records interface="Products.CMFPlone.interfaces.controlpanel.IFilterSchema" prefix="plone">
    <value key="custom_attributes" remove="true">
      <element>slot</element>
    </value>
 </records>

or like this

<records interface="Products.CMFPlone.interfaces.controlpanel.IFilterSchema" prefix="plone">
    <value key="custom_attributes">
      <element remove="true">slot</element>
    </value>
 </records>

[mauritsvanrees]

I saw this today as well, Plone 6.0.0b1.
Some extra code would be needed around these lines:
https://github.com/plone/plone.app.registry/blob/2.0.0a9/plone/app/registry/exportimport/handler.py#L271-L273

In my case I am trying to remove a table style from TinyMCE. The node_value here is:

<value key="table_styles" purge="false">
    <element remove="true">HighChart grafiek|highchart</element>
</value>

This gets translated to value ['HighChart grafiek|highchart']

[Rudd-O]

How did we go 20 years without this haha.