This guideline is a part of the English Wikipedia's Manual of Style.
|This page in a nutshell: Hidden text, that is visible only when editing, can be inserted into articles, project pages, and other Wikipedia pages, by surrounding the text as follows:
|Manual of Style (MoS)|
On Wikipedia, hidden text is text that is visible when editing the source for the page or when using VisualEditor, but not on the "rendered" version of the page presented to readers of the article.
Invisible comments are useful for alerting other editors to issues such as common mistakes that regularly occur in the article, a section title's being the target of an incoming link, or pointing to a discussion that established a consensus relating to the article. They should not be used to instruct other editors not to perform certain edits, although where existing local consensus is against making such an edit, they may usefully draw the editor's attention to that. Avoid adding too many invisible comments because they can clutter the wiki source for other editors.