Explain what is DTD (Document Type Declaration)? Mention what is the difference between CDATA and PCDATA in DTD?

A DTD means Document Type Definition (DTD) which defines the structure, legal elements and attributes of an XML document.
 PCDATA: A PCDATA is a Parsed Character Data. XML parsers usually parse all the text in an XML document.
 CDATA: While CDATA is an Unparsed Character Data, the term CDATA is used about text data that should not be parsed by the XML parser.

Explain what is long polling?

Long polling is a web application development pattern used to emulate pushing data from the server to the client. When the long polling is used, the client sends a request to the server, and the connection remains intact until the server is ready to send data to the client. The connection will be closed only after the data is sent back to the client or connection timeout occurs.

Explain what is an ETag and how does it work?

An ETag is an opaque identifier allocated by a web server to a specific version of a resource found at a URL. The ETag is a part of HTTP, the protocol for the world wide web and when the server reads the ETag from client request, the server can then tell whether to send the file (HTTP 200) or tell the client just to use their local copy (HTTP 304).

List out the advantage of HTTP/2 as compared with HTTP 1.1?

The advantage of HTTP/2 compared to HTTP/1.1 is
 HTTP headers data compression
Server push technologies
 Over a single TCP connection parallel loading of page elements
 Prioritization of request

Explain what is CORS? How does it work?

(CORS) Cross-Origin Resource Sharing is a mechanism that enables many resources (e.g., JavaScript, fonts etc.) on a web page to be requested from another domain outside the domain from which the resource originated. It is a mechanism supported in HTML5 that manages XMLHttpRequest access to a domain different.

What web developer should know?

A good web developer should know
 HTML
CSS
SQL
PHP/Ruby/Python
JQuery
JavaScript

Explain what are the key responsibilities of a Web Developer?

Program test and debug all web applications
Design, develop, test and deploy web applications
Uploading sites onto server and registering it with different search engines
Coordinate with other designers and programmers to develop web projects
Fix bugs, troubleshoot and resolve problems
 In case of system failure initiate periodic testing and implement contingency plans
Develop appropriate code structures to solve specific tasks
Support and assist in the upkeep and maintenance of websites
Assume ownership of code throughout staging, development, testing and production