Mahapps - How to set Proper Case in Titles

New versions:

Window Title

<controls:MetroWindow x:Class="MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
  TitleCharacterCasing="Normal" />

GroupBox

Set a style (option 1) or set a property (option 2)

<!-- Option 1 -->
<Style TargetType="{x:Type GroupBox}" BasedOn="{StaticResource MetroGroupBox}">
    <Setter Property="Controls:ControlsHelper.ContentCharacterCasing" Value="Normal" />
</Style>

<!-- Option 2 -->
<GroupBox Controls:ControlsHelper.ContentCharacterCasing="Normal" />

Credits: @Suplanus & @Oscar Vicente Perez

---

Old versions:

To set window title case:

Set the TitleCaps property on your MetroWindow to false.

<controls:MetroWindow x:Class="MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  TitleCaps="False" />

To use title case in groupbox:

Put that TextBlock in the GroupBox's header.

<GroupBox>
  <GroupBox.Header>
    <TextBlock Text="My Group Box"/>
  </GroupBox.Header>
  Some content
</GroupBox>

TitleCaps="False" is obsolete, use this code in the Window:

TitleCharacterCasing="Normal"