It is not one of Wikipedia's policies or guidelines; rather, its purpose is to explain certain aspects of Wikipedia:Citing sources. It may reflect differing levels of consensus and vetting.
Shortcut
WP:REFDD
Referencing is key to making Wikipedia reliable and trustworthy.
When working with references:
DO:
Use inline citations (either footnotes or shortened footnotes).
Keep citations near the material they support, e.g. after the sentence.
Say where in the source the information came from.
Use a consistent reference style within each article.
Consider using citation templates to create a consistent style.
Tag under-sourced material with an appropriate inline tag.
Tag under-sourced articles with an appropriate header.
DON'T:
Don't rely on unreliable sources.
Don't cite a source you haven't seen for yourself.
Don't add material that's not supported by sources.
Don'tplace external links in the body of articles.
Don't add references for obvious information.
Don't use all-numeric date formats other than YYYY-MM-DD.
Don't change an established reference style without consensus.
See alsoedit
Help:Referencing for beginners
Help:Referencing for beginners without using templates
Help:Referencing for beginners with citation templates