Use the AllowMark property to show on the control's vertical scroll bar the positions of expressions in the text. Use the MarkColor property to specify a marking color for an expression. Use the AddKeyword to add new keywords to the control's context. Use the AddExpression to add new expressions to the control. By default, the AllowMark property is False. If the AllowMark property is True, the control could load the text slowly, because each line requires to be parsed in order to find the expression to be highlighted on the control's vertical scroll bar, so we would suggest to use this option only before you check the time to load the file using this option. Use the MarkContinueBlocks property to mark multiple lines block. Use the Refresh method to refresh the control's visible area, when adding expressions on the fly. 

The following VB sample defines the // TODO expressions, and marks on the control's vertical scroll bar each position of the // TODO expression in the control's text:

With Edit1
    .AllowMark = True
    .AddExpression "<fgcolor=000080>// TODO</fgcolor>", "<b><fgcolor=000080> </fgcolor></b>", ""
    .MarkColor("// TODO") = RGB(0, 0, &H80)
    .Refresh
End With

As you can see from the following screen shot, there are lines ( on the control's vertical scroll bar ) that marks the position for each // TODO expression in the text.

The following C++ sample marks the position of the // TODO expressions on the control's vertical scroll bar:

COleVariant vtMissing; vtMissing.vt = VT_ERROR;
m_edit.SetAllowMark( TRUE );
m_edit.AddExpression("<fgcolor=000080>// TODO</fgcolor>", "<fgcolor=000080> </fgcolor>", "", vtMissing, vtMissing );
m_edit.SetMarkColor("// TODO", RGB(0, 0, 0x80) );
m_edit.Refresh();

The following VB.NET sample marks the position of the // TODO expressions on the control's vertical scroll bar:

With AxEdit1
    .AllowMark = True
    .LineNumberWidth = -1
    .AddExpression("<fgcolor=000080>// TODO</fgcolor>", "<b><fgcolor=000080> </fgcolor></b>", "")
    .set_MarkColor("// TODO", ToUInt32(Color.FromArgb(0, 0, &H80)))
    .CtlRefresh()
End With

where the ToUInt32 function converts a Color expression to an OLE_COLOR expressions:

Shared Function ToUInt32(ByVal c As Color) As UInt32
    Dim i As Long
    i = c.R
    i = i + 256 * c.G
    i = i + 256 * 256 * c.B
    ToUInt32 = Convert.ToUInt32(i)
End Function

The following C# sample marks the position of the // TODO expressions on the control's vertical scroll bar:

axEdit1.AllowMark = true;
axEdit1.AddExpression("<fgcolor=000080>// TODO</fgcolor>", "<b><fgcolor=000080> </fgcolor></b>", "");
axEdit1.set_MarkColor("// TODO", ToUInt32(Color.FromArgb(0, 0, 0x80)));
axEdit1.CtlRefresh();

where the ToUInt32 function converts a Color expression to an OLE_COLOR expressions:

private UInt32 ToUInt32(Color c)
{
	long i;
	i = c.R;
	i = i + 256 * c.G;
	i = i + 256 * 256 * c.B;
	return Convert.ToUInt32(i);
}

The following VFP sample marks the position of the // TODO expressions on the control's vertical scroll bar:

With thisform.Edit1.Object
	.AllowMark = .t.
	.AddExpression("<fgcolor=000080>// TODO</fgcolor>", "<b><fgcolor=000080> </fgcolor></b>", "")
	.MarkColor("// TODO") = RGB(0, 0, 128)
	.Refresh
EndWith