{tikz-arrows} is about questions related to the arrow head specifications in the arrows library of the TikZ/PGF graphics package. If the question is not specifically addressing an issue related to the arrow construction, use the general {tikz-pgf} tag.
In TikZ/PGF package, one can find the Arrow Tip library for a variety of custom arrow heads. To be able to utilize these extra arrowheads, the following line
\usetikzlibrary{arrows}
should be added to the preamble. Then the arrowheads can be used in the TikZ pictures with, for example,
\draw[right hook reversed-open diamond] (0,0) -- (2,2);
which results in
See Tikz/PGF manual for more comprehensive details.
