Fixes #3724 (#3768)

Add a remark that the regular expression searches for an exact match and how to do a search hit.

Author: SheepRock

xml/System.ComponentModel.DataAnnotations/RegularExpressionAttribute.xml

@@ -37,7 +37,9 @@
       <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- You apply the RegularExpressionAttribute attribute to a property when you need to validate values for the property against a regular expression. The regular expression enables you to specify very precisely the format of valid values. The Pattern property contains the regular expression.If the value of the property is null or an empty string (""), the value automatically passes validation for the RegularExpressionAttribute attribute. To validate that the value is not `null` or an empty string, use the **RequiredAttribute** attribute.  
+ You apply the RegularExpressionAttribute attribute to a property when you need to validate values for the property against a regular expression. The regular expression enables you to specify very precisely the format of valid values. The Pattern property contains the regular expression. If the value of the property is null or an empty string (""), the value automatically passes validation for the RegularExpressionAttribute attribute. To validate that the value is not `null` or an empty string, use the **RequiredAttribute** attribute. 
+
+The regular expression searches for an exact match, not using `^` before and `$` at the end of the pattern produces the same results as using it. For a search hit, prepend and append the pattern with `.*`.