In tag files,does attribute values accept expressions or not? If not please explain the reason

**Actually when i do manually in tomcat server with out eclipse it's working,but in eclipse it is raising the following exception.... could any body explain this please............**

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: /demo1.jsp(20,5) According to TLD or attribute directive in tag file, attribute value does not accept any expressions org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40) org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407) org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:148) org.apache.jasper.compiler.Validator$ValidateVisitor.checkXmlAttributes(Validator.java:952) org.apache.jasper.compiler.Validator$ValidateVisitor.visit(Validator.java:706) org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1442) org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2166) org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2216) org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2222) org.apache.jasper.compiler.Node$Root.accept(Node.java:457) org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2166) org.apache.jasper.compiler.Validator.validate(Validator.java:1484) org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:167) org.apache.jasper.compiler.Compiler.compile(Compiler.java:296) org.apache.jasper.compiler.Compiler.compile(Compiler.java:277) org.apache.jasper.compiler.Compiler.compile(Compiler.java:265) org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:564) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:302) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

note The full stack trace of the root cause is available in the Apache Tomcat/5.5.26 logs.

Apache Tomcat/5.5.26