not all modern implementations have implemented this specification correctly (e.g., Safari)

Hence an email address/mailbox/addr-spec is "local-part@domain"; "local-part" is composed of one or more of 'word' and periods; "word" can be an "atom" which can include anything except "specials", control characters or blank/space; and specials (the *only* printable ASCII characters [other than space, if you call space "printable"] *excluded* from being a valid "local-part") are: ()<>@,;:\".[] Therefore by the official standard for email on the internet, the plus sign is as much a legal character in the local-part of an email address as "a" or "_" or "-" or most any other symbol you see on the main part of a standard keyboard.

"+" is a completely valid character in an email address; as defined by the internet messaging standard published in 1982(!) RFC 822 (page 8 & 9)... Any website claiming anything else is wrong by definition, plus they are prohibiting me and many fellow anti-spam activists from tracking where inbound spam comes from:

never care and try to understand design standards

The Gmail Android app that comes pre-installed with most new Android phones contains a feature to access non-Google accounts using POP and IMAP. Unfortunately, emails accessed through this setup lack the embedded style (<style>) support as well as the support for background images.

overflow-wrap: break-word; makes sure the long string will wrap and not bust out of the container. You might as well use word-wrap as well because as the spec says, they are literally just alternate names for each other. Some browsers support one and not the other.

I personally think that starting from google's components makes easier to keeping update to material specs updates.

All browers handle 302 incorrectly. Chrome 30, IE10. It became the de facto incorrect implementation; that cannot be changed because so many web-sites issue mistakenly issue 302. In fact ASP.net MVC incorrectly issues 302, depending on the fact that browsers handle it incorrectly.

The problem is that opting out of mime type negotiation simply because there is a catch-all in there is wrong according to the specifications of HTTP.