When this document speaks of [Definition: Strong TLS algorithms], then the following must hold:
No version of the TLS protocol that suffers known security flaws has been negotiated. At the point of writing of this document, versions of SSL prior to SSLv3 [SSLv3] MUST NOT be considered strong.
A cipher suite has been selected for which key and algorithm strengths correspond to industry practice. At the time of writing of this document, the "export" cipher suites explicitly forbidden in appendix A.5 of [TLSv11] MUST NOT be considered strong.

[32] 1121706 – Firefox 35.0 security.ssl3 Problem - Unable to connect to Google (2015-09-24 20:35:43 +09:00 版) https://bugzilla.mozilla.org/show_bug.cgi?id=1121706

[33] Issue 442572 - chromium - Disable AES-256-CBC modes by default - An open-source project to help move the web forward. - Google Project Hosting (2015-09-27 00:55:36 +09:00 版) https://code.google.com/p/chromium/issues/detail?id=442572

[34] 1113974 – Disable AES-256-CBC modes by default (2015-09-27 00:55:51 +09:00 版) https://bugzilla.mozilla.org/show_bug.cgi?id=1113974

[35] 1084554 – Implement TLS 1.2 DHE AES-GCM cipher suites (2015-09-27 11:12:31 +09:00 版) https://bugzilla.mozilla.org/show_bug.cgi?id=1084554

[37] What cipher suites does CloudFlare use for SSL? – CloudFlare Support (2015-06-30 07:58:00 +09:00 版) https://support.cloudflare.com/hc/en-us/articles/200933580-What-cipher-suites-does-CloudFlare-use-for-SSL-

[38] API Deprecations and Removals in Chrome 53 | Web Updates - Google Developers ( (2016-08-11 18:27:47 +09:00)) https://developers.google.com/web/updates/2016/08/chrome-53-deprecations#dhe-based-ciphers-being-phased-out

[39] mod_http2 - Apache HTTP Server Version 2.4 ( (2017-01-15 21:40:17 +09:00)) https://httpd.apache.org/docs/2.4/mod/mod_http2.html#H2ModernTLSOnly

The security checks require that the TSL protocol is at least TLSv1.2 and that none of the ciphers listed in RFC 7540, Appendix A is used. These checks will be extended once new security requirements come into place.
The name stems from the Security/Server Side TLS definitions at mozilla where "modern compatibility" is defined. Mozilla Firefox and other browsers require modern compatibility for HTTP/2 connections. As everything in OpSec, this is a moving target and can be expected to evolve in the future.

[40] Editorial: spell cypher as cipher (foolip著, 2017-12-20 18:39:26 +09:00) https://github.com/whatwg/fetch/commit/0b6c2b170be77ba1f889a7ff25b7e181f5dc1524

[41] Editorial: spell cypher as cipher by foolip · Pull Request #649 · whatwg/fetch (2017-12-21 11:47:35 +09:00) https://github.com/whatwg/fetch/pull/649

[42] Editorial: spell cyphertext ciphertext (annevk著, 2017-12-20 19:08:31 +09:00) https://github.com/whatwg/html/commit/81656488e77d37b177ffd27272cddb36416e226e

[43] Editorial: spell cyphertext ciphertext by annevk · Pull Request #3307 · whatwg/html (2017-12-21 11:51:04 +09:00) https://github.com/whatwg/html/pull/3307

[44] SSL ciphers, 2020-09-21T09:01:13.000Z, 2020-10-01T05:57:44.742Z https://curl.haxx.se/docs/ssl-ciphers.html

[45] curl - How To Use, 2020-09-21T09:01:13.000Z, 2020-10-01T06:27:53.735Z https://curl.haxx.se/docs/manpage.html#--proxy-ciphers

[46] Deprecating TLS v1.0 and v1.1 | Slack (Slack, 2021-01-30T03:07:53.000Z) https://api.slack.com/changelog/2019-07-deprecate-early-tls-versions#what

TLS connections must support at least one of the following supported cipher suites:
ECDHE-RSA-AES128-GCM-SHA256
ECDHE-RSA-AES256-GCM-SHA384
ECDHE-RSA-AES128-SHA
ECDHE-RSA-AES256-SHA
AES128-GCM-SHA256
AES256-GCM-SHA384

[47] Using the Slack Web API | Slack (Slack, 2021-01-30T03:08:19.000Z) https://api.slack.com/web#ssl

TLS connections must support at least one of the following supported cipher suites:
ECDHE-RSA-AES128-GCM-SHA256
ECDHE-RSA-AES256-GCM-SHA384
ECDHE-RSA-AES128-SHA256
ECDHE-RSA-AES256-SHA384