When the major version is zero, the caret's "left-most non-zero component" moves inward, and the bound tightens. Today you handle the 0.x and 0.0.x cases that make caret genuinely tricky.
Expand "^0.2.3" into ">=0.2.3 <0.3.0" and "^0.0.3" into ">=0.0.3 <0.0.4".
A 0.x version means “not stable yet,” and SemVer treats a leading zero as a
signal that anything might change, so caret gets stricter. The rule is still
“do not modify the left-most non-zero component,” but when the major is 0 that
component is no longer the major. For ^0.2.3 the left-most non-zero component is
the minor, so caret pins the minor and allows only patch changes:
>=0.2.3 <0.3.0. For ^0.0.3 even the minor is zero, so the left-most non-zero
component is the patch, and caret allows nothing but that exact patch onward
to the next one: >=0.0.3 <0.0.4.
This is the case that makes caret worth understanding rather than memorizing. The
same operator that admitted an entire major line for ^1.2.3 admits only a single
patch for ^0.0.3, purely because of where the first non-zero digit sits. Extend
the caret desugaring with the two zero branches: if the major is zero and the minor
is not, bump the minor; if both are zero, bump the patch. With that, caret is
complete and behaves exactly as every npm-based project depends on it to.
// Upper bound bumps whichever is the LEFT-MOST NON-ZERO component:// MAJOR != 0 -> <(MAJOR+1).0.0 (last lesson)// MAJOR == 0, MINOR != 0 -> <0.(MINOR+1).0// MAJOR == 0, MINOR == 0 -> <0.0.(PATCH+1)// "^0.2.3" -> [ >=0.2.3 , <0.3.0 ] ; "^0.0.3" -> [ >=0.0.3 , <0.0.4 ]