/fill replace syntax is not updated
The syntax for /fill in the help menu (/help fill or just /fill) will show:
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] [oldBlockHandling] [dataTag]
However, when [oldBlockHandling] is replace, you can optionally choose a block where [dataTag] would be which would only replace that block type with the block in <TileName>. The help syntax for /fill does not accommodate for that optional feature and there should be a separate syntax for /fill replace:
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] [oldBlockHandling] [replacedTile]
or
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] replace [replacedTile]
Environment
Mac OS X 10.8.5
Processor: 2.5 GHz Intel Core i5
Memory: 4GB 1600 MHz DDR3
Java: 1.6.0_65 (64 bit)
Linked Issues
Created Issue:
/fill replace syntax is not updated
The syntax for /fill in the help menu (/help fill or just /fill) will show:
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] [oldBlockHandling] [dataTag]
However, when [oldBlockHandling] is replace, you can optionally choose a block where [dataTag] would be which would only replace that block type with the block in <TileName>. The help syntax for /fill does not accommodate for that optional feature and there should be a separate syntax for /fill replace:
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] [oldBlockHandling] [replacedTile]
or
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [DataValue] replace [replacedTile]
Environment
Mac OS X 10.8.5
Processor: 2.5 GHz Intel Core i5
Memory: 4GB 1600 MHz DDR3
Java: 1.6.0_65 (64 bit)
relates to
is duplicated by
Note: This bug and another bug that I posted, MC-66531, are greatly linked and should both be seen together.

Note: This bug and another bug that I posted,
MC-66920, are greatly linked and should both be seen together.Confirmed for 1.8.
This will be updated once I find time to fix the behavior to be consistent for all types of blocks. Right now block entity blocks can't be replaced, while all other blocks can.