Regulare Expressions

USER Name:
Accept username, user_name, username_123,
Not accept user name, 123Username, _username,

ControlToValidate="TextBoxUserId" Display="None" SetFocusOnError="True"runat="server" ErrorMessage="Invalid User name"meta:resourcekey="REVUserNameResource1">

USER PASSWORD:
Display="None" SetFocusOnError="True" ValidationExpression="(?!^[0-9@,|()[\]{}#.$%&_'*+:;^`'~?=!-]*$)(?!^[a-zA-Z@,|()[\]{}#.$%&_'*+:;^`'~?=!-]*$)^([a-zA-Z0-9@,|()[\]{}#.$%&_'*+:;^`'~?=!-]{6,25})$"
ControlToValidate="TextBoxPassword" meta:resourcekey="RegularExpressionValidator5Resource1">

CITY NAME:
Accept New yourk not accep numaric,special characters

ValidationExpression="^[a-zA-Z\s]{1,40}$" runat="server" Display="None" ErrorMessage="Enter Only Character"
meta:resourcekey="REVTextBoxCityNameResource1">

BLOOD GROPUP :
ErrorMessage="Enter Valid Blood Group." Display="None" runat="server"
meta:resourcekey="REVTextBoxBloodGroupResource1">

RESTICATED EXTENSIONS:
ErrorMessage="Can't upload exe or msi" Display="None">
LIMIT IN TEXT AREA
Display="None" ErrorMessage="Limit Exceed"
SetFocusOnError="True" ValidationExpression="(.|\r|\n){0,10}">

// valid date format for exp (mm/dd/yyyy )
//This R.E used for validate date with leap year I used this in javascript :
var RegExPattern = /^(?=\d)(?:(?:(?:(?:(?:0?[13578]|1[02])(\/|-|\.)31)\1|(?:(?:0?[1,3-9]|1[0-2])(\/|-|\.)(?:29|30)\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})|(?:0?2(\/|-|\.)29\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))|(?:(?:0?[1-9])|(?:1[0-2]))(\/|-|\.)(?:0?[1-9]|1\d|2[0-8])\4(?:(?:1[6-9]|[2-9]\d)?\d{2}))($|\ (?=\d)))?(((0?[1-9]|1[012])(:[0-5]\d){0,2}(\ [AP]M))|([01]\d|2[0-3])(:[0-5]\d){1,2})?$/;
if(EntredDate.match(RegExPattern) == null)//If entred date is not matched then show message
{
arguments.IsValid = false;
return false;//show error message
}