You can search dances for patterns of figures. This somewhat dated video walks you through it.
The dance matches if and only if (iff) there is a figure somewhere in the dance.
The dance matches iff it's formation matches.
Matches iff all the subexpressions match the dance.
Matches iff any of the subexpressions match the dance.
Matches iff the subexpression does not match the dance.
Most queries are for the presence or absence of a thing - the thing appears either 0 times or 1 time in the dance. Count lets you specify numbers of times other than 0 or 1 to check for the query.
Like and, but the subexpressions have to match in the order they
appear in the dance, directly abuting each other. For example, You can
use this to check for dances with a roll away immediately followed by
a swing, whereas with and you could only check to see if the dance
had both a roll away and a swing.
Note: this search wraps around the end of the dance, so allemande then allemande will match a dance where the first and last figures
are allemandes.
then gets more interesting when it's subexpressions are more than
simple figures - e.g. not and all, but for that we need a more
complicated understanding of queries.
Up until now, it's been possible to think of each query matching or not matching on a dance as a whole. But in order to do more complicated queries, we'll need to think of a query matching or not matching on the dance as a whole and also on sets of consecutive figures (here called 'patches', but not called that in the source code).
If a query doesn't match a dance, then it can have no matching
patches. A query can match a dance, and match zero or more patches -
we'll see an example of a dance matching with zero figures with and,
below.
Patches 1 figure long, equal to that figure, match.
The dance matches if any subexpression matches. The matched patches are the unions of the subexpressions' matched patches.
The dance matches if all the subexpressions match. Individual patches match if they're matched by each subexpression.
It's common to have a matching dance that has zero matching
subexpressions. E.g. chain and hey will match lots of dances, but
since no single figure is both a chain and a hey, no figures will ever
match.
Like and, but the dance will only match if there is at least one
matching patch.
Count matches the patches of it's subexpression, if it matches at
all. Note that some combinations of count and then are kind-of
non-useful, such as: "swing then count chain ≥ 2" means "A swing
followed by a chain, and - oh yeah - the dance has to have two
chains".
The dance matches iff the subexpression doesn't match. If the dance matches, then all 1-figure-long patches match.
This is important if you're using then: swing then no hey will
match the same dances as swing and no hey - likely not what you
intended.
What we were maybe trying to get in the previous example was a search
for dances that had a swing followed by any move besides a hey, but
that were still allowed to have heys elsewhere in the dance. Enter
not. not matches all figures (length-1 patches)+ that are not matched
by their subexpression. swing then not hey - will match dances with a
swing followed by any figure not a hey.
not was formerly called 'anything but'.
The dance matches only if every figure matches - this isn't too
practical, and anyway all figure x is equivalent to not no figure x, but it seems somehow to complete the set. Here's one possible
application: imagine teaching contra to a preschool, and you want to
find only dances with certain figures. You could use: all (swing or allemande or circle or do si do or star or ...) to search for dances
that use only simple moves.