using System; using System.Collections.Generic; using System.Text; namespace TextSpanExample { class Program { static void Main(string[] args) { string document = "The COVID-19 pandemic has caused a global health crisis."; var keyword = "COVID-19"; var index = document.IndexOf(keyword); var textSpan = new TextSpan(index, keyword.Length); var fullText = document.Substring(textSpan.Start, textSpan.Length); Console.WriteLine(fullText); } } }In this example, the code first searches for the keyword within the document using the IndexOf() method. It then creates a new TextSpan object based on the starting index of the keyword and its length. Finally, it extracts the full text of the TextSpan using the Substring() method and outputs it to the console. The TextSpan Covering feature is included in the System.Text namespace of the .NET Core library.