This is a sample action that shows how to extract additional info for the content selection when working with Trados Studio Integarion API.

ContentSelectionSample.cs

using Sdl.Desktop.IntegrationApi;
using Sdl.Desktop.IntegrationApi.Extensions;
using Sdl.TranslationStudioAutomation.IntegrationApi;
using System;
using System.Text;
using System.Windows.Forms;

namespace CurrentSelectionSample.RibbonAction
{
    [Action(Id = "SelectionSample", Name = "Test Me", Icon = "CursorIcon")]
    [ActionLayout(typeof(SelectionSample), 10, DisplayType.Large)]
    public class Selection : AbstractAction
    {
        protected override void Execute()
        {
            //Obtain the editor controll together with the current active document. The editor might
            //have multiple documents opened but only one is active.
            
            var editorController = SdlTradosStudio.Application.GetController<EditorController>();
            var activeDocument = editorController.ActiveDocument;

            //pass the current selection to the methods that will extract all the new
            //selection information
            
            ShowSelectionInfo(activeDocument.Selection);

        }

        private void ShowSelectionInfo(DocumentSelection documentSelection)
        {
            //Selection can be done in both source and target and this sample 
            //is demonstrating that this is working in the same way for both

            var details = new StringBuilder();
            details.AppendLine("Source selection details");
            var sourceSelection = documentSelection.Source;
            details.AppendLine(ShowContentSelection(sourceSelection));

            details.AppendLine("Target selection details");
            var targetSelection = documentSelection.Target;
            details.AppendLine(ShowContentSelection(targetSelection));


            MessageBox.Show(details.ToString());
        }

        private string ShowContentSelection(AbstractContentSelection selection)
        {
            var details = new StringBuilder();

            //Information like IsEmpty, IsReversed and IsValid are available general
            //details available for the text selection

            details.AppendLine("    Selection empty: " + (selection.IsEmpty ? "Yes" : "No"));
            details.AppendLine("    Selection reversed: " + (selection.IsReversed ? "Yes" : "No"));
            details.AppendLine("    Selection valid: " + (selection.IsValid ? "Yes" : "No"));

            //Besides the above general information each content/text selection can have has 
            //a starting (From) and ending (UpTo) point which are marked with more details and this required 
            //because a selection can span on multiple segments. This is why From has a row number, cursor position,
            //and segment id which can be different from the details in the UpTo
            
            details.AppendLine("    From Details: ");
            var fromDetails = selection.From;
            details.Append(ShowSelectionInfoDetails(fromDetails));
            details.AppendLine("    Upto Details: ");
            var upToDetails = selection.UpTo;
            details.Append(ShowSelectionInfoDetails(upToDetails));
            return details.ToString();
        }

        private string ShowSelectionInfoDetails(ContentSelectionInfo fromDetails)
        {
            var details = new StringBuilder();
            if (fromDetails != null)
            {
                details.AppendLine("        Row Number: " + fromDetails.RowNumber);
                details.AppendLine("        Cursor Position: " + fromDetails.CursorPosition);
                details.AppendLine("        Segment Id: " + fromDetails.SegmentId);
            }
            return details.ToString();
        }
    }
}