renovate/lib/modules/versioning/composer/readme.md

Composer uses Semver-like versioning, but some package authors may use versions that are not completely valid, e.g. 1.2 instead of 1.2.0.

Composer supports ranges in a similar manner to npm, but not identical. The main difference is with tilde ranges.

Tilde ranges with "short" versions are different to npm. e.g.

~4 is equivalent to ^4 in npm ~4.1 is equivalent to ^4.1 in npm ~0.4 is equivalent to >=0.4 <1 in npm

Composer supports patches in the version numbers, which are considered stable. E.g., 1.2.3-p1 is recognized by npm as unstable, Renovate implements additional logic to support correct sorting and stability checks on composer patch versions syntax.