This section describes some of the terminology used throughout the rest of this document. Although the code slush is not a hard freeze on the tree, the &team.re; requests that bugs in the existing code base take priority over new features. The code slush does not enforce commit approvals to the branch. The code freeze marks the point in time where all commits to the branch require explicit approval from the &team.re;. The &os; Subversion repository contains several hooks to perform sanity checks before any commit is actually committed to the tree. One of these hooks will evaluate if committing to a particular branch requires specific approval. To enforce commit approvals by the &team.re;, the Release Engineer updates base/svnadmin/conf/approvers, and commits the change back to the repository. Once this is done, any change to the branch must include an Approved by: line in the commit message. The Approved by: line must match the second column in base/svnadmin/conf/approvers, otherwise the commit will be rejected by the repository hooks. During the code freeze, &os; committers are urged to follow the Change Request Guidelines. KBI/KPI stability implies that the caller of a function across two different releases of software that implement the function results in the same end state. The caller, whether it is a process, thread, or function, expects the function to operate in a certain way, otherwise the KBI/KPI stability on the branch is broken.