programaticaly setting grid width as a string, ie: "auto" or "*", "10", or "*2", or "*3", etc : Here's what i'm trying to do:

XAML:

    <local:MegaGrid MegaRow="auto,auto,*">
        <Button Grid.Row="0" Content="btn1"/>
        <Button Grid.Row="1" Content="btn2"/>
        <Button Grid.Row="2" Content="btn3 stretch"/>
    </local:MegaGrid>

C#:

    public class MegaGrid : Grid
    {
        private string zMegaRow = "";
    
        public string MegaRow(string RowSetterString) 
        {
            get {return zMegaRow;}
            set {
                zMegaRow = value;
                RowDefinitions.Clear();
    
                string[] items = value.Split(", \t");
    
                foreach (string item in items)
                {
                    RowDefinitions.Add(
                      **??? How to Convert "value" string into a RowDefinition???**
                    });
                }
            }
        }
    }

What I need to know, is how to call the same String to RowDefinitions converter that the XAML uses to create the RowDefintions object.  Except to invoke it from C# instead of from XAML. 
