// Methods that get the index of first match; otherwise return null
public static int?FindFirstIndex(this TextRow row, string sought) =>
row.FindFirstIndex(sought, StringComparison.Ordinal);
public static int?FindFirstIndex(this TextRow row,
string sought, StringComparison comparison) =>
row.FindFirstIndex(s => string.Equals(s, sought, comparison));
public static int GetFirstIndex(this TextRow row, Func <string, bool> predicate) =>
row.FindFirstIndex(predicate) is int i ? i : throw new InvalidOperationException("Sequence contains no elements.");