MapServer wms_layer_group, set title

Question

We want to group wms layers in mapfiles and give the group a title that is different from the name. Until now we did this with GROUP and wms_group_title, but GROUP is deprecated and we want to use "wms_layer_group" instead. But there we have the problem that we can't set the title of the group, obviously wms_layer_group doesn't work here. In get_capabilities the title is always just the same as the name of the group. How can we set the title of the group?

with GROUP:

LAYER
    NAME a
    GROUP group_ab
    ...
    METADATA
        wms_title "title of a"
        wms_group_title "title of group_ab"
    ...
    
LAYER
    NAME b
    GROUP group_ab
    ...
    METADATA
        wms_title "title of b"
        wms_group_title "title of group_ab"
    ...

Get_capabilities:

<Name>group_ab</Name>
<Title>title of group_ab</Title>
    <Name>a</Name>
    <Title>title of a</Title>
    <Name>b</Name>
    <Title>title of b</Title>

with wms_layer_group:

LAYER
    NAME a
    METADATA
      "wms_layer_group" "/group_ab/a"
      "wms_title" "title of a"
      "wms_group_title" "title of group_ab"
    ...
    
LAYER
    NAME b
    METADATA
      "wms_layer_group" "/group_ab/b"
      "wms_title" "title of b"
      "wms_group_title" "title of group_ab"
    ...

Get_capabilities:

<Name>group_ab</Name>
<Title>group_ab</Title>
    <Name>a</Name>
    <Title>title of a</Title>
    <Name>b</Name>
    <Title>title of b</Title>