Regular Expression tester http://www.regextester.com/
I can’t express the importance of using web standards enough, hopefully the following articles and resources can.
10 Reasons to Learn and Use Web Standards - If you’re a web developer or designer new to the concept of web standards and are undecided on whether you should spend the time to learn all about them or not, here are some of the most important reasons for doing so. For web professionals who are already using web standards, this list may come in handy when you need good arguments.
Developing With Web Standards - This document explains how and why using web standards will let you build websites in a way that saves time and money for the developer and provides a better experience for the visitor. Also discussed are other methods, guidelines and best practices that will help produce high-quality websites that are accessible to as many as possible.
10 Reason for Web Standards - 10 more reasons to develop with web standards.
Roadmap to Standards
The Web Standards Project - The Web Standards Project is a grassroots coalition fighting for standards that ensure simple, affordable access to web technologies for all.
Web Standards Workshop
The Guild of Accessible Web Designers - GAWDS is a world-wide association of organisations and accessible web designers and developers - designed to both promote and protect standards - not technical standards - but accessible design standards.
Now that you’re all caught up on standards make sure you always validate your code to make sure it’s compliant. These tools from W3C will also help you find any errors so you know what needs to be fixed.
HTML & XHTML Validator