Back in the 2000s, it was commonplace to see websites that were built using Flash. By viewing the source of a website, you’d often see very little HTML and an embedded SWF file. This meant a few things. First, the browser didn’t natively support Flash, so you had to download the Flash plugin. Browsers found it difficult to go into the SWF to read content. Amongst other things, this had a detrimental affect on SEO and accessibility.