* Negative discrepancy is allowed and handled correctly

* Exclude SHFB output in gitignore
* More documentation

Author: RobThree

.gitignore

@@ -194,3 +194,6 @@ FakesAssemblies/
 
 # Visual Studio 6 workspace options file
 *.opt
+
+# Sandcastle Helpfilebuilder output
+*.chm

TwoFactorAuth.Net.Tests/TwoFactorAuthTests.cs

@@ -103,6 +103,13 @@ public void VerifyCodeWorksCorrectly()
             Assert.IsTrue(target.VerifyCode("VMR466AB62ZBOKHE", "543160", 2, 1426847205 - 65));	    // Test discrepancy
         }
 
+        [TestMethod]
+        public void VerifyCodeAllowsNegativeDiscrepancy()
+        {
+            var target = new TwoFactorAuth(null, 6, 30, Algorithm.SHA1);
+            Assert.IsTrue(target.VerifyCode("VMR466AB62ZBOKHE", "543160", -2, 1426847205 - 65));	    // Test negative discrepancy
+        }
+
 
         [TestMethod]
         public void VerifyTotpUriIsCorrect()

TwoFactorAuth.Net/Providers/Qr/BaseHttpQrCodeProvider.cs

@@ -57,6 +57,8 @@ public abstract class BaseHttpQrCodeProvider
         /// </summary>
         /// <param name="baseUri">The base Uri for the QR code provider.</param>
         /// <param name="sslPolicy">The <see cref="SslPolicy"/> to be used by the QR code provider.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="baseUri"/> is null.</exception>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when an invalid <see cref="SslPolicy"/> is specified.</exception>
         protected BaseHttpQrCodeProvider(Uri baseUri, SslPolicy sslPolicy)
         {
             if (baseUri == null)

TwoFactorAuth.Net/Providers/Qr/GoogleQrCodeProvider.cs

@@ -64,6 +64,9 @@ public GoogleQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, int margi
         /// <param name="errorCorrectionLevel">The <see cref="ErrorCorrectionLevel"/> to use when generating QR codes.</param>
         /// <param name="marginRows">The width of the white border around the data portion of the code.</param>
         /// <param name="sslPolicy">The <see cref="SslPolicy"/> to use when generating QR codes.</param>
+        /// <exception cref="ArgumentOutOfRangeException">
+        /// Thrown when an invalid <see cref="ErrorCorrectionLevel"/> is specified or marginRows is less than 0.
+        /// </exception>
         public GoogleQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, int marginRows, SslPolicy sslPolicy)
             : base(baseuri, sslPolicy)
         {

TwoFactorAuth.Net/Providers/Qr/QRicketQrCodeProvider.cs

@@ -119,6 +119,9 @@ public QRicketQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, Color ba
         /// <param name="foregroundColor">The foreground color to be used for the QR code.</param>
         /// <param name="imageFormat">The <see cref="QRicketImageFormat"/> of the QR code.</param>
         /// <param name="sslPolicy">The <see cref="SslPolicy"/> to use when generating QR codes.</param>
+        /// <exception cref="ArgumentOutOfRangeException">
+        /// Thrown when an invalid <see cref="ErrorCorrectionLevel"/> or <see cref="QRicketImageFormat"/> is specified.
+        /// </exception>
         public QRicketQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, Color backgroundColor, Color foregroundColor, QRicketImageFormat imageFormat, SslPolicy sslPolicy)
             : base(baseuri, sslPolicy)
         {
@@ -139,6 +142,9 @@ public QRicketQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, Color ba
         /// </summary>
         /// <returns>Returns the MIME type of the image.</returns>
         /// <seealso cref="IQrCodeProvider"/>
+        /// <exception cref="InvalidOperationException">
+        /// Thrown when an unknown <see cref="QRicketImageFormat"/> is used.
+        /// </exception>
         public string GetMimeType()
         {
             switch (this.ImageFormat)

TwoFactorAuth.Net/Providers/Qr/QrServerQrCodeProvider.cs

@@ -190,6 +190,11 @@ public QrServerQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, int mar
         /// <param name="foregroundColor">The foreground color to be used for the QR code.</param>
         /// <param name="imageFormat">The <see cref="QrServerImageFormat"/> of the QR code.</param>
         /// <param name="sslPolicy">The <see cref="SslPolicy"/> to use when generating QR codes.</param>
+        /// <exception cref="ArgumentOutOfRangeException">
+        /// Thrown when an invalid <see cref="ErrorCorrectionLevel"/> or <see cref="QrServerImageFormat"/> is specified,
+        /// <paramref name="margin"/> is less than 0 or more than 50 or <paramref name="quietZone"/> is less than 0 or
+        /// more than 100.
+        /// </exception>
         public QrServerQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, int margin, int quietZone, Color backgroundColor, Color foregroundColor, QrServerImageFormat imageFormat, SslPolicy sslPolicy)
             : base(baseuri, sslPolicy)
         {
@@ -219,6 +224,9 @@ public QrServerQrCodeProvider(ErrorCorrectionLevel errorCorrectionLevel, int mar
         /// </summary>
         /// <returns>Returns the MIME type of the image.</returns>
         /// <seealso cref="IQrCodeProvider"/>
+        /// <exception cref="InvalidOperationException">
+        /// Thrown when an unknown <see cref="QrServerImageFormat"/> is used.
+        /// </exception>
         public string GetMimeType()
         {
             switch (this.ImageFormat)

TwoFactorAuth.Net/Providers/Rng/HashRngProvider.cs

@@ -26,6 +26,7 @@ public HashRngProvider()
         /// Initializes a new instance of the <see cref="HashRngProvider"/> with a specified <see cref="HashAlgorithm"/>.
         /// </summary>
         /// <param name="algorithm">The <see cref="HashAlgorithm"/> to use when generating random number sequences.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="algorithm"/> is null.</exception>
         public HashRngProvider(HashAlgorithm algorithm)
         {
             if (algorithm == null)