Question

I have a textbox :

<asp:RegularExpressionValidator ID="ValidateTitleCharacters" runat="server" 
    ValidationExpression="^[a-zA-Z0-9@+'.!#$',:;=/\(\),\-\s]{1,255}$"
    ControlToValidate="title" Text="You have entered a character(s) that is not allowed in the title."
    ErrorMessage="You have entered a character(s) that is not allowed in the title." />

I want to allow ” character also. How can I modify the regular expression string???

I tried this:

<asp:RegularExpressionValidator ID="ValidateTitleCharacters" runat="server" 
    ValidationExpression="^[a-zA-Z0-9@+'.!#$'\",:;=/(),\-\s]{1,255}$"
    ControlToValidate="title" Text="You have entered a character(s) that is not allowed in the title."
    ErrorMessage="You have entered a character(s) that is not allowed in the title." />

<asp:RegularExpressionValidator ID="ValidateTitleCharacters" runat="server" 
    Validat‌​ionExpression="^[a-zA-Z0-9@+'.!#$',:;=/()(""),\-\s]{1,255}$"
    ControlToValidate="title" Text="You have entered a character(s) that is not allowed in the title."
    ErrorMessage="You have entered a character(s) that is not allowed in the title." />

Both attempts are breaking the string.

Answer 1

From the fragment you have posted, it appears that the regular expression is embedded in markup – this means you need to escape the double quote character as an HTML character entity.

Use ":

ValidationExpression="^[a-zA-Z0-9@+'.!#$'",:;=/\(\),\-\s]{1,255}$"

The ASP.NET engine will translate the character entity to ".

Alternatively, set the ValidationExpression value in code behind (in OnInit, for example):

ValidateTitleCharacters.ValidationExpression = 
                                  "^[a-zA-Z0-9@+'.!#$'\",:;=/\(\),\-\s]{1,255}$";