In its simplest form, a search expression just contains a string to be search for with the help of a full-text search. For example, the string syntax will search for all zettel containing the word “syntax”.
If you want to search for all zettel with a title containing the word “syntax”, you must specify title:syntax. “title” denotes the metadata key, in this case the supported metadata key “title”. The colon character (“:”) is a search operator, in this example to specify a match. “syntax” is the search value that must match to the value of the given metadata key, here “title”.
A search expression may contain more than one search term, such as title:syntax. Search terms must be separated by one or more space characters, for example title:syntax title:search. All terms of a select expression must be true so that a zettel is selected.
Above sequence of search expressions may be combined by specifying the keyword OR. At most one of those sequences must be true so that a zettel is selected.