Thank you for adding getAttachedFace()!
I forgot to mention it in my bug (https://hub.spigotmc.org/jira/browse/SPIGOT-6388), but I've been using reflection to access this field as well for 3+ years and it's really nice to have a Bukkit/Spigot API alternative for the future

`isOpen()`, `isClosed()` and `isPeeking()` are redundant, `getPeek()` is enough. Checking if it is either open, closed or peeking can be achieved using `getPeek()`. In regards to why it is implemented as a float rather than a byte, a link to the pull request below in which this was discussed.

^{https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/pull-requests/821/overview}

You should provide Methods like isOpen() or isClosed() and also isPeeking() for Users that don't want to find out if Peeking is 50.0 or 100,0 with your Methods. (Also why do you implemented the 'peeking' as Percentage and not with the bytes it rly uses^^)

I will look into adding the attached face to the API as well.

Implemented in Shulker:

public boolean isPeeking();
public boolean isClosed();
public boolean isOpen();
public void setPeeking();
public void setOpen();
public void setClosed();
public void setCustomPeek(byte b);
public BlockFace getAttachedFace();
public void setAttachedFace(BlockFace bf);

(SpigotMC Contributor Licensing is done too)

0102 is from Spigot\CraftBukkit-Patches
0016 is from Spigot\Bukkit-Patches