The package builds on the standard LaTeX packages graphics
and/or graphicx and allows external LaTeX source files to be
included, in the same way as graphic files, by
\includegraphics. In effect, then package adds support for the
.tex extension. Some of the lower level operations like
clipping and trimming are implemented using the adjustbox
package which includes native pdfLaTeX support and uses the pgf
package for other output formats.