function isSubsequenceString( prop ) {
	// TODO: consider whether to make this check more robust (e.g., should we actually throw if someone tries to access `foo:bar`? If we make this check more exact, how would we distinguish between a non-existent `foo:bar` property and an actual error in the subsequence string?)
	return RE_SUBSEQ.test( prop );
}
Tests if an indexing expression is a subsequence.

@private
@param {string} prop - property name
@returns {boolean} result

@example
var out = isSubsequenceString( '::-2' );
// returns true

@example
var out = isSubsequenceString( '10,1,::-1,:,-5,2::3' );
// returns true

@example
var out = isSubsequenceString( '...' );
// returns false

@example
var out = isSubsequenceString( '-2' );
// returns false