If no paragraph is selected in the control, setting this property applies the alignment setting to the paragraph in which the insertion point appears as well as to paragraphs created after the paragraph that has the alignment property setting. For example, if there are two paragraphs in a System.Windows.Forms.RichTextBox control and the insertion point is located within the second paragraph. If you set the RichTextBox.SelectionAlignment property to HorizontalAlignment.Center, the paragraph at the insertion point will be centered within the control. If a third paragraph is created after the second paragraph, it also is aligned to the center of the control.

If a selection is made within the control when the property is set, all paragraphs selected are aligned based on this property setting. You can use this property to align the paragraphs in a document being created in the System.Windows.Forms.RichTextBox. For example, if you want all paragraphs in a document to be centered, you can select all the paragraphs in the control and set the RichTextBox.SelectionAlignment property to HorizontalAlignment.Center.