74
`:<dst>` means to update the same ref as the `<src>`.
75
+
76
The object referenced by <src> is used to update the <dst> reference
77
-on the remote side. By default this is only allowed if <dst> is not
78
-a tag (annotated or lightweight), and then only if it can fast-forward
79
-<dst>. By having the optional leading `+`, you can tell Git to update
80
-the <dst> ref even if it is not allowed by default (e.g., it is not a
81
-fast-forward.).
82
-+
83
-Pushing an empty <src> allows you to delete the <dst> ref from
84
-the remote repository.
77
+on the remote side. Whether this is allowed depends on where in
78
+`refs/*` the <dst> reference lives as described in detail below, in
79
+those sections "update" means any modifications except deletes, which
80
+as noted after the next few sections are treated differently.
81
++
82
+The `refs/heads/*` namespace will only accept commit objects, and
83
+updates only if they can be fast-forwarded.
84
++
85
+The `refs/tags/*` namespace will accept any kind of object (as
86
+commits, trees and blobs can be tagged), and any updates to them will
87
+be rejected.
88
++
89
+It's possible to push any type of object to any namespace outside of
90
+`refs/{tags,heads}/*`. In the case of tags and commits, these will be
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+treated as if they were the commits inside `refs/heads/*` for the
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+purposes of whether the update is allowed.
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++
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+I.e. a fast-forward of commits and tags outside `refs/{tags,heads}/*`
95
+is allowed, even in cases where what's being fast-forwarded is not a
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+commit, but a tag object which happens to point to a new commit which
97
+is a fast-forward of the commit the last tag (or commit) it's
98
+replacing. Replacing a tag with an entirely different tag is also
99
+allowed, if it points to the same commit, as well as pushing a peeled
100
+tag, i.e. pushing the commit that existing tag object points to, or a
101
+new tag object which an existing commit points to.
102
++
103
+Tree and blob objects outside of `refs/{tags,heads}/*` will be treated
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+the same way as if they were inside `refs/tags/*`, any update of them
105
+will be rejected.
106
++
107
+All of the rules described above about what's not allowed as an update
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+can be overridden by adding an the optional leading `+` to a refspec
109
+(or using `--force` command line option). The only exception to this
110
+is that no amount of forcing will make the `refs/heads/*` namespace
111
+accept a non-commit object. Hooks and configuration can also override
112
+or amend these rules, see e.g. `receive.denyNonFastForwards` in
113
+linkgit:git-config[1] and`pre-receive` and `update` in
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+linkgit:githooks[5].
115
++
116
+Pushing an empty <src> allows you to delete the <dst> ref from the
117
+remote repository. Deletions are always accepted without a leading `+`
118
+in the refspec (or `--force`), except when forbidden by configuration
119
+or hooks. See `receive.denyDeletes` in linkgit:git-config[1] and
120
+`pre-receive` and `update` in linkgit:githooks[5].
121
+
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The special refspec `:` (or `+:` to allow non-fast-forward updates)
123
directs Git to push "matching" branches: for every branch that exists on