ant-design-blazor/components/select/internal/SelectOptionGroup.razor

@namespace AntDesign.Select.Internal
@inherits AntDomComponentBase
@typeparam TItemValue
@typeparam TItem

@{
    RenderFragment<SelectOptionItem<TItemValue, TItem>> selectOptionFragment = (model) => 
        @<SelectOption
            @key="@model.InternalId"
            TItemValue="TItemValue"
            TItem="TItem">
        </SelectOption>;
}

@foreach (var selectOption in SelectParent.SortedSelectOptionItems)
{
    if (_oldGroupName == selectOption.GroupName)
    {
        <CascadingValue Value="@selectOption.InternalId" Name="InternalId">
            @selectOptionFragment(selectOption)
        </CascadingValue>
    }
    else
    {
        <div class="@ClassMapper.Class">@selectOption.GroupName</div>
        <CascadingValue Value="@selectOption.InternalId" Name="InternalId">
            @selectOptionFragment(selectOption)
        </CascadingValue>
        
        _oldGroupName = selectOption.GroupName;
    }   
}