In a recent python-ideas thread, the rule of dunder methods being reserved for Python internal usage only was brought up (https://mail.python.org/archives/list/python-ideas@python.org/message/GMRPSSQW3SXNCP4WU7SYDINL67M2WLQI/), due to an author of a third party library using them without knowing better. Steven D'Aprano linked the following section of the docs that defines the rule: https://docs.python.org/3/reference/lexical_analysis.html#reserved-classes-of-identifiers. 

When I had attempted to search for the rule in the documentation (prior to the above discussion), I noticed that it was rather difficult to discover because it was written just as "System-defined names" with no mention of "dunder" (which is what the dev community typically refers to them as, at least in more recent history).

To make it easier for the average user and library maintainer to locate this section, I propose changing the first line to one of the following:

1) System-defined names, also known as "dunder" names.
2) System-defined names, informally known as "dunder" names.

I'm personally in favor of (1), but I could also see a reasonable argument for (2). If we can decide on the wording, it would make for a good first-time PR to the CPython docs.

I vote for #2.   It improves findability while also recognizing that "dunder" isn't a formal term and lies somewhere between slang and jargon.

> I vote for #2.   It improves findability while also recognizing that "dunder" isn't a formal term and lies somewhere between slang and jargon.

Yeah, I suppose it is a bit more of a slang or jargon term rather than something with a formal definition, so (2) is fine with me. Thanks for the feedback. 

I'll leave the issue open for a new contributor as it would be an easy PR to work on. But, if it doesn't receive any attention within a few months or so, I'll likely just add it myself since it would be useful to me for easily locating the section in the future.

Hi, I'm ready to work on this.

New changeset 5f9c131c099d6675d1a9d0228497865488afd548 by Javad Mokhtari in branch 'master':
bpo-40045: Make "dunder" method documentation easier to locate (#19153)
https://github.com/python/cpython/commit/5f9c131c099d6675d1a9d0228497865488afd548

New changeset bb852266b77ffeeb09a42847c907829eec6d5cb5 by Miss Islington (bot) in branch '3.8':
bpo-40045: Make "dunder" method documentation easier to locate (GH-19153) (GH-19198)
https://github.com/python/cpython/commit/bb852266b77ffeeb09a42847c907829eec6d5cb5

New changeset c3622b2dcc9278900a7e3cbef12edfa83a8728ed by Miss Islington (bot) in branch '3.7':
bpo-40045: Make "dunder" method documentation easier to locate (GH-19153) (GH-19199)
https://github.com/python/cpython/commit/c3622b2dcc9278900a7e3cbef12edfa83a8728ed

I think this is resolved. Someone can re-open if they feel discontent. Thanks @javadmokhtari for the patch.

This issue has been resolved (thanks to @javadmokhtari and @nanjekyejoannah), but its Status is still "open" and the Resolution is blank...
Members of Python triage team, please change the Status to "closed" and  the Resolution to "fixed".
Thank you!

Closing as fixed. Thanks Hilit.