Adobe InDesign - Manual (Page 275)

to deselect it.
Nonprinting characters such as those for spaces, tabs, ends of paragraphs, index markers, and ends of stories appear. These special characters
are visible only in a document window and a story editor window; they don’t print or output to formats such as PDF and XML. The hidden
characters appear in the same color as the layer color.
Nonprinting characters hidden (top) and visible (bottom)
Anne Marie Concepcion provides a comprehensive list of special characters at Free Guide to InDesign Special Characters .
List of hidden characters
Hidden character What it represents
End of Paragraph
Soft return (line break)
Space
End of Story
Discretionary Hyphen
Nonbreaking Hyphen
Tab
Right Indent Tab
Indent to Here
End Nested Style Here
Non-Joiner
Ideographic Space
Em Space
En Space
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