The <c:out< tag evaluates an expression and writes its value to the output stream. The syntax of the tag is as follows:

<c:out value=”TagValue”>
default value
</c:out>

The attributes of the <c:out> tag are as follows:

• value: This is a mandatory attribute. It declares the expression to be evaluated.
• escapeXml: This is an optional attribute that determines whether characters <, >, &, ‘, and ” in the resulting string should be converted to their corresponding character entity codes.
  
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The element is used to modify the XML declaration property of the output of a JSP document or tag file. This action can be used only in the JSP documents and in tag files that are in XML syntax. The XML declaration property in JSP2.0 can only be modified. All attributes of the are optional but some of them depend upon other attributes. This attribute contains the following attributes:

1. omit-xml-declaration: It is used to specify a value of true or yes and omits the XML declaration.
2. doctype-root-element: It indicates the root element of the XML document in the DOCTYPE.

The element is an optional element of the deployment descriptor. It maps the location of a tag library descriptor (TLD) with a URI pattern.
When deploying a Web application, a separate element is used for each TLD.
The element has the following sub-elements:

• : It describes the location of the file name in the TLD, relative to the root of the Web application.
• : It describes a URI, relative to the location of the web.xml document, identifying a Tag Library used in the Web application.

Authentication is the process of verifying the identity of a user. This is usually done using a user name and a password. This process compares the provided user name and password with those stored in the database of an authentication server.

There are four types of authentication as follows:

1. BASIC: It transmits data over the network and hence is not much secure.
2. DIGEST: It transmits data in the hashed form.
3. CLIENT-CERT: It transmits data in the form of public key certificates. It is a secure method but is rarely used, as it requires that consumers have certificates.