iOS 中的要求是：
三位数字：x.x.x
主版本号：主要更新，新功能
次版本号：次要更新，次功能
维护发布版本号：
Configuring Your Xcode Project for Distribution
“The version number is a two-period-separated list of positive integers, as in 4.5.2. The first integer represents a major revision, the second a minor revision, and the third a maintenance release. ”
“CFBundleShortVersionString
The release version number is a string comprised of three period-separated integers. The first integer represents major revisions to the app, such as revisions that implement new features or major changes. The second integer denotes revisions that implement less prominent features. The third integer represents maintenance releases.
CFBundleVersion
CFBundleVersion (String – iOS, OS X) specifies the build version number of the bundle, which identifies an iteration (released or unreleased) of the bundle. The build version number should be a string comprised of three non-negative, period-separated integers with the first integer being greater than zero. The string should only contain numeric (0-9) and period (.) characters. Leading zeros are truncated from each integer and will be ignored (that is, 1.02.3 is equivalent to 1.2.3). This key is not localizable.
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Configuring Your Xcode Project for Distribution
“The build string represents an iteration (released or unreleased) of the bundle and is also a two-period-separated list of positive integers, as in 1.2.3.”