In Obsidian.md, my notes viewer/editor, it is possible to add YAML frontmatter to each note. This is content ignored when a note is displayed and is used to add metadata to a note. The Dataview plugin allows one to query such metadata to display selected lists of such notes. (‘Show me all notes in the folder ‘Books’ where status=read’)

I don’t much like to use YAML, because it can quickly turn into a chore to add them, if you come to depend on them to create overviews and indexes etc.
Dataview also allows me to add datafields inside the actual text of the note. This is already better because whatever else happens, the datafields are within the text of the note itself and can be read there in context. (YAML frontmatter is also inside the note, but separate from the main body of text of the notes, not in context.)

YAML frontmatter is added like this:
---
fieldname:value
fieldname2:anothervalue
---

Adding fields in the main body of the note for Dataview requires using a double colon (::)
Fieldname::value

However when I try to use the latter option, or switch the location of data from the YAML frontmatter to fields included in the main body of a note, the Dataview query returns zero results. I’m not sure why that is, or what I’m doing wrong.