Sometime we require a condition where we need to add html tags in <appSettings> value.
If we directly  add html tags in value then it gives the syntax error. To resolve this we need to add html tags in encoded form.
Here, below is the example of this:

1. Use encoded html - for "<" use &lt; and for ">" use &gt;
eg:

In C#.NET

web.config:

<add key="example" value="Hi, &lt;br&gt; &lt;/br&gt; This is a C# example. " />

.cs file

string s= Convert.ToString(ConfigurationManager.AppSettings("example"));

then s will return as

Hi,

This is a C# example.

In VB.NET

web.config:

<add key="example" value="Hi, &lt;br&gt; &lt;/br&gt; This is a VB example. " />

.vb file

Dim s As String
s=Convert.ToString(ConfigurationManager.AppSettings("example"))

then s will return as

Hi,

This is a VB example.

Hope this code will help you. Thanks