[DXCategory("Events")]
public event TextEditCustomHighlightTextEventHandler CustomHighlightText

<DXCategory("Events")>
Public Event CustomHighlightText As TextEditCustomHighlightTextEventHandler

using DevExpress.XtraEditors;

// Enable Advanced Mode during the control's initialization (for instance, at design time)
memoEdit1.Properties.UseAdvancedMode = DevExpress.Utils.DefaultBoolean.True;

memoEdit1.Text = "The formation of a star begins with gravitational instability within a molecular cloud, caused by regions of higher density—often triggered by compression of clouds by radiation from massive stars \r\n (Wikipedia)";
memoEdit1.Font = new Font("Tahoma", 10);

private void memoEdit1_CustomHighlightText(object sender, TextEditCustomHighlightTextEventArgs e) {
    // Change a word's background color and add padding.
    e.HighlightWords("with", (block) => {
        block.BackColor = Color.Yellow;
        block.Padding = new Padding(5, 0, 5, 0);
    });

    // Change a string's background and foreground colors.
    e.HighlightRanges("cloud", (block) => {
        block.BackColor = Color.Yellow;
        block.ForeColor = Color.Red;
    });

    // Strikethrough text at the beginning of the first line.
    if (e.LineIndex == 0)
        e.HighlightRange(0, 12, (block) => { block.Painter = new MyStrikethroughTextPainter(Color.Gray); });

    // Draw a star icon instead of the 'star' string.
    e.HighlightRanges(
        "Star",
        (block) => {
            block.Painter = new MyImagePainter();
            block.ContentSize = new Size(14, 14);
            block.AllowNavigation = false;
        },
        System.Globalization.CompareOptions.IgnoreCase);
}

public class MyStrikethroughTextPainter : TextEdit.TextEditBlockPainter {
    public MyStrikethroughTextPainter(Color color) {
        Color = color;
    }
    Color Color { get; set; }
    static readonly Font StrikeoutFont = new Font("Tahoma", 10f, FontStyle.Strikeout);
    public override bool DrawForeground(TextEdit.Block block) {
        DrawString(block.Text, StrikeoutFont, block.Segments[0].TextBounds, Color);
        return true;
    }
}

public class MyImagePainter : TextEdit.TextEditBlockPainter {
    static Bitmap img;
    static Bitmap Image {
        get {
            if (img == null) {
                using (var temp = System.Drawing.Image.FromFile("d:\\star.png"))
                    img = new Bitmap(temp);
            }
            return img;
        }
    }
    public override bool DrawForeground(TextEdit.Block block) {
        DrawBitmap(Image, block.Segments[0].Bounds, new RectangleF(Point.Empty, Image.Size));
        return true;
    }
}

Imports DevExpress.XtraEditors

' Enable Advanced Mode during the control's initialization (for instance, at design time).
MemoEdit1.Properties.UseAdvancedMode = DevExpress.Utils.DefaultBoolean.True

MemoEdit1.Text = "The formation of a star begins with gravitational instability within a molecular cloud, caused by regions of higher density—often triggered by compression of clouds by radiation from massive stars " & Constants.vbCrLf & " (Wikipedia)"
MemoEdit1.Font = New Font("Tahoma", 10)

Private Sub MemoEdit1_CustomHighlightText(sender As Object, e As DevExpress.XtraEditors.TextEditCustomHighlightTextEventArgs) Handles MemoEdit1.CustomHighlightText
    ' Change a word's background color and add padding.
    e.HighlightWords("with", Sub(block)
                                    block.BackColor = Color.Yellow
                                    block.Padding = New Padding(5, 0, 5, 0)
                                End Sub)
    ' Change a string's background and foreground colors.
    e.HighlightRanges("cloud", Sub(block)
                                    block.BackColor = Color.Yellow
                                    block.ForeColor = Color.Red
                                End Sub)

    ' Strikethrough text at the beginning of the first line.
    If e.LineIndex = 0 Then e.HighlightRange(0, 12, Sub(block)
                                                        block.Painter = New MyStrikethroughTextPainter(Color.Gray)
                                                    End Sub)

    ' Draw a star icon instead of the 'star' string.
    e.HighlightRanges("Star", Sub(block)
                                    block.Painter = New MyImagePainter()
                                    block.ContentSize = New Size(14, 14)
                                    block.AllowNavigation = False
                                End Sub, System.Globalization.CompareOptions.IgnoreCase)
End Sub

Public Class MyStrikethroughTextPainter
    Inherits TextEdit.TextEditBlockPainter

    Public Sub New(ByVal color As Color)
        color = color
    End Sub

    Private Property Color As Color
    Shared ReadOnly StrikeoutFont As Font = New Font("Tahoma", 10F, FontStyle.Strikeout)

    Public Overrides Function DrawForeground(ByVal block As TextEdit.Block) As Boolean
        DrawString(block.Text, StrikeoutFont, block.Segments(0).TextBounds, Color)
        Return True
    End Function
End Class

Public Class MyImagePainter
    Inherits TextEdit.TextEditBlockPainter

    Shared img As Bitmap

    Private Shared ReadOnly Property Image As Bitmap
        Get
            If img Is Nothing Then
                Using temp = System.Drawing.Image.FromFile("d:\star.png")
                    img = New Bitmap(temp)
                End Using
            End If

            Return img
        End Get
    End Property

    Public Overrides Function DrawForeground(ByVal block As TextEdit.Block) As Boolean
        DrawBitmap(Image, block.Segments(0).Bounds, New RectangleF(Point.Empty, Image.Size))
        Return True
    End Function
End Class