Analogy: mathematical expressions
This mechanism is similar to mathematical formulas: a big formula
is created by composing small formulas. Such formulas are called
expressions, and they can contain other expressions, so you can
make arbitrarily complex and large expressions. For example,
| | 1
1 + 2
(1 + 2) * 3
((1 + 2) * 3) / (4 * 5)
|
This is a sequence of expressions, where each expression is
contained in the next (larger) one. The simplest expressions are
numbers, and larger ones are made by combining expressions with
operators (like +, *, and /) and parentheses.
Like mathematical expressions, music expressions can be nested
arbitrarily deep, which is necessary for complex music like
polyphonic scores.