This allows a linked SplitPanels to be dynamically expanded and collapsed by clicking on the splitter button, and resized by dragging the splitter.

Add right to left support.

This should be the same as in the standard split container – the panels should be swapped.

To reproduce:

Add a RadSplitContainer with several SplitPanels and use the following code:
  this.radSplitContainer1.EnableCollapsing = true;
  this.radSplitContainer1.UseSplitterButtons = true;

If you run the project, you will notice that the next/previous buttons are displayed for manipulating the SplitPanel's collapsed/expanded state. If you click one of the next/previous buttons, the relevant SplitPanel will be collapsed and the splitter will remain visible. Thus, the user has the possibility to return the previous state of the SplitPanel. However, if you try to collapse the SplitPanel programmatically by setting the Collapsed property to true, the corresponding splitter will disapper.

Use attached to reproduce. Move the splitter with the mouse and you will notice that is position is not correct when the mouse is released

When you cut-copy RadSplitContainer containing two SplitPanels from one form to another, only the RadSplitContainer is pasted, but the SplitPanels are missing.

Add functionality to collapse and expand the split panels in RadSplitContainer by buttons positioned in the splitter area just like ASP.NET. See example here: 
http://demos.telerik.com/aspnet-ajax/splitter/examples/collapseexpand/defaultcs.aspx

The Modifiers property should be visible in the properties window when a SplitPanel instance is selected. 

Workaround:

Manually change the modifier in the Designer.cs file to protected.
  

Workaround: check the attached project

SplitPanel - there is no property Name in Visual Studio designer.

If the AutoScroll of RadSplitContainer is true and I scroll the container a little, don’t work the resizes of the panels.

sample code:

public Form1()
    {
        InitializeComponent();
 
        RadSplitContainer radSplitContainer1 = new RadSplitContainer()
        {
            Dock = DockStyle.Fill,
            AutoScroll = true
        };
 
        this.Controls.Add(radSplitContainer1);
 
        for (int i = 0; i < 10; i++)
        {
            var panel = new SplitPanel();
            panel.SizeInfo.SizeMode = SplitPanelSizeMode.Absolute;
            panel.SizeInfo.AbsoluteSize = new Size(100, 0);
            radSplitContainer1.SplitPanels.Add(panel);
        }
    }

The scenario that we want to cover is to disable resizing the split panels but still enable the option for expanding/collapsing them via the buttons.

To reproduce:
- Use relative sizing and save the RelativeRatio.
- Set the same value after restarting the application.
- The panel size is not the same. 

Workaround:
Use absolute size. 

In this particular case, the main monitor has 125% DPI. When showing a RadForm which contains RadSplitContainer with 2 panels, the control is not scaled correctly.

Expected:

Current behavior:

Workaround:

Set the RadControl.EnableRadAutoScale property to false.

When you drop a RadSplitContainer in a RadDock ToolWindow, RadSplitContainer loses important options from its SmartTag's ActionMenu.
Similar behavior is obtained when you drag a RadSplitContainer from the ToolBox and drop it onto an empty RadDock.

Let's have a RadSplitContainer on a form. This RadSplitContainer should contain two SplitPanels and one splitter. Change the color of the splitter using the Edit UI Elements dialog. Run the project and you will get IndexOutOfRangeException. However, if you cut and paste the designer code in the form_load, it will work correctly.

To reproduce:
- Add button to a split panel
- Set button Text property to "Button &X"
- Add a event handler for the button
- Start the application and press the "x" key

To work around this issue instead of using mnemonics you can set shortcuts like this:
radButton.ButtonElement.Shortcuts.Add(new RadShortcut(Keys.Alt, Keys.X));

Also you can set mnemonic like underline like this:
radButton.Text = "<html>Button <u>X";

In design time when trying to copy-paste a RadSplitContainer, which contains a couple panels, it throws exception.

Steps to reproduce:
Add a RadSplitContainer to a form or user control.
Add a couple of panels to the container using the designer.
Press Ctrl+A to select all the controls on the form or user control.
Press Ctrl+C to copy them to the clipboard.
Create a new form or user control (this step isn't strictly necessary, but helps explain the issue).
Paste the controls on the clipboard into the new form or user control using Ctrl+V