/// <summary>
        /// Learns a program to extract the surname from a given table row (rather than a whole document).
        /// </summary>
        public static void LearnSurnameWithRespectToTableRow()
        {
            string    s   = File.ReadAllText(Path.Combine(_sampleDocs, "sample-document-1.html"));
            HtmlDoc   doc = HtmlDoc.Create(s);
            WebRegion referenceRegion1 = doc.GetRegion("tr:nth-child(1)");                 //1st table row
            WebRegion exampleRegion1   = doc.GetRegion("tr:nth-child(1) td:nth-child(2)"); //2nd cell in 1st table row
            WebRegion referenceRegion2 = doc.GetRegion("tr:nth-child(2)");                 //2nd table row
            WebRegion exampleRegion2   = doc.GetRegion("tr:nth-child(2) td:nth-child(2)"); //2nd cell in 2nd table row
            CorrespondingMemberEquals <WebRegion, WebRegion> exampleSpec1 = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion1, exampleRegion1);
            CorrespondingMemberEquals <WebRegion, WebRegion> exampleSpec2 = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion2, exampleRegion2);

            Web.RegionProgram prog = Web.RegionLearner.Instance.Learn(new[] { exampleSpec1, exampleSpec2 });
            if (prog == null)
            {
                return;
            }
            //run the program on 5th table row
            WebRegion fifthRowRegion = doc.GetRegion("tr:nth-child(5)"); //5th table row
            WebRegion region         = prog.Run(new [] { fifthRowRegion })?.SingleOrDefault();

            Console.WriteLine("Learn surname with respect to table row: ");
            Console.WriteLine(region.GetSpecificSelector());
            Console.WriteLine(region.Text());
            Console.WriteLine();
        }
        /// <summary>
        /// Learns a program to extract the first surname in the document from two examples
        /// from two different documents.
        /// </summary>
        public static void LearnFirstSurnameInDocumentUsingMultipleExamples()
        {
            string    s1               = File.ReadAllText(Path.Combine(_sampleDocs, "sample-document-1.html"));
            HtmlDoc   doc1             = HtmlDoc.Create(s1);
            string    s2               = File.ReadAllText(Path.Combine(_sampleDocs, "sample-document-2.html"));
            HtmlDoc   doc2             = HtmlDoc.Create(s2);
            WebRegion referenceRegion1 = new WebRegion(doc1);
            WebRegion referenceRegion2 = new WebRegion(doc2);
            WebRegion exampleRegion1   = doc1.GetRegion("tr:nth-child(1) td:nth-child(2)"); //2nd cell in 1st table row of doc1
            WebRegion exampleRegion2   = doc2.GetRegion("tr:nth-child(1) td:nth-child(2)"); //2nd cell in 1st table row of doc2
            CorrespondingMemberEquals <WebRegion, WebRegion> exampleSpec1 = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion1, exampleRegion1);
            CorrespondingMemberEquals <WebRegion, WebRegion> exampleSpec2 = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion2, exampleRegion2);

            Web.RegionProgram prog = Web.RegionLearner.Instance.Learn(new[] { exampleSpec1, exampleSpec2 });
            if (prog == null)
            {
                return;
            }
            //run the program on the second document
            WebRegion region = prog.Run(new [] { referenceRegion2 })?.SingleOrDefault();

            Console.WriteLine("Learn first surname in document from multiple examples: ");
            Console.WriteLine(region.GetSpecificSelector());
            Console.WriteLine(region.Text());
            Console.WriteLine();
        }
        /// <summary>
        /// Learns a program to extract the first surname in the document from one example.
        /// </summary>
        public static void LearnFirstSurnameInDocumentUsingOneExample()
        {
            string    s               = File.ReadAllText(Path.Combine(_sampleDocs, "sample-document-1.html"));
            HtmlDoc   doc             = HtmlDoc.Create(s);
            WebRegion referenceRegion = new WebRegion(doc);
            WebRegion exampleRegion   = doc.GetRegion("tr:nth-child(1) td:nth-child(2)"); //2nd cell in 1st table row
            CorrespondingMemberEquals <WebRegion, WebRegion> exampleSpec = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion, exampleRegion);

            Web.RegionProgram prog = Web.RegionLearner.Instance.Learn(new[] { exampleSpec });
            if (prog == null)
            {
                return;
            }
            //run the program to extract first surname from the document
            WebRegion region = prog.Run(new [] { referenceRegion })?.SingleOrDefault();

            Console.WriteLine("Learn first surname in document from one example: ");
            Console.WriteLine(region.GetSpecificSelector());
            Console.WriteLine(region.Text());
            Console.WriteLine();
        }
        /// <summary>
        /// Learns a program to extract the surname from a given table row (rather than a whole document)
        /// using a negative example.
        /// </summary>
        public static void LearnSurnameWithRespectToTableRowUsingNegativeExample()
        {
            string    s   = File.ReadAllText(Path.Combine(_sampleDocs, "sample-document-1.html"));
            HtmlDoc   doc = HtmlDoc.Create(s);
            WebRegion referenceRegion1 = doc.GetRegion("tr:nth-child(1)"); //1st table row
            WebRegion referenceRegion2 = doc.GetRegion("tr:nth-child(2)"); //2nd table row
            var       posExampleSpec   = new CorrespondingMemberEquals <WebRegion, WebRegion>(referenceRegion1, doc.GetRegion("tr:nth-child(1) td:nth-child(2)"));
            var       negExampleSpec   = new CorrespondingMemberDoesNotEqual <WebRegion, WebRegion>(referenceRegion2, doc.GetRegion("tr:nth-child(2) td:nth-child(1)"));

            Web.RegionProgram prog = Web.RegionLearner.Instance.Learn(new Constraint <IEnumerable <WebRegion>, IEnumerable <WebRegion> >[] { posExampleSpec, negExampleSpec });
            if (prog == null)
            {
                return;
            }
            WebRegion region = prog.Run(new [] { referenceRegion1 })?.SingleOrDefault();

            Console.WriteLine("Learn surname with respect to table row using negative example: ");
            Console.WriteLine(region.GetSpecificSelector());
            Console.WriteLine(region.Text());
            Console.WriteLine();
        }