In the old days, pages were written separately for supporting different browsers. It means that if you were developing a website in the early days of the internet, you would have written code separately for chrome and firefox. To solve this problem, standards were developed by W3C but browsers could not have started supporting the new standards at once as it would have broken most of the websites at that time. Therefore, different rendering modes were developed for supporting new standard-compliant sites as well as old legacy sites.
Layout Engine now uses three different rendering modes in web browsers:
- Quirks modes: Layout emulates non-standard behavior as supported by old browsers.
- Almost standard modes: A small number of quirks/old behavior are supported while rendering the layout.
- Full standard modes: Layout emulates standard behavior as described by HTML and CSS specifications.