Why ajax editor not getting validated when I change Font or color

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ASP.NET

Ajax

Hi all I used ajax editor control in my application with a regular expression as follows

<cc1:Editor ID="Editor1"  runat="server" />
<asp:RegularExpressionValidator ID="regexpEditor" ValidationGroup="subj" runat="server"
ErrorMessage="Description must be of 20 characters" ControlToValidate="Editor1"
ValidationExpression="[A-Za-z0-9#,.\-_ ]{20,}" />

But when I change font color or if i enter some links or as per posted the question description with some html tags, I am getting the validator fired. How can I use as per my requirement to fulfill the conditions

1) Atlease 20 characters has to be entered it may be links or some other.
2) If I changeFont color and size and it should get validated.

What ever we can do in an editor control all should get validated