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+# iftex
+
+## TeX Engine Detection
+
+This iftex package provides a suite of commands for detecting
+different TeX variants.
+
+For each supported engine, tests are provided of the form
+
+ \ifpdftex which is true if PDFTeX is in use and \RequirePDFTeX
+ which stops the run with an error message if PDFTeX is not being used.
+
+The package (which works with plain TeX as well as LaTeX) has tests
+for:
+
+eTeX, PDFTeX, XeTeX, LuaTeX, LuaHBTeX, pTeX, upTeX, pTeX-ng, VTeX, Aleph.
+
+
+In addition, an \iftutex test is true for XeTeX and LuaTeX, and
+an \ifpdf test is provided to test the PDF or DVI output mode.
+
+## Compatibility Packages
+
+In addition to the main iftex.sty package, small wrapper packages are
+provided
+
+ifetex.sty  ifluatex.sty  ifvtex.sty  ifxetex.sty ifpdf.sty
+
+These include iftex and in some cases emulate some additional
+commands to allow these packages to replace the original packages in TeX
+distributions. It is recommended that new documents do not use these
+packages, but instead load iftex.sty directly.
+
+This package may be used on any format (it may be loaded into initex)
+it does not assume LaTeX.
+
+
+----
+
+This is a merger and simplification of several packages
+Based on a suggestion of Norbert Preining
+
+https://github.com/bidi-tex/iftex/issues/1
+
+
+ * ifetex: Martin Scharrer
+ * ifxetex: Will Robertson
+ * iftex:  Persian TeX Group / Vafa Khalighi
+ * ifluatex, ifvtex: Heiko Oberdiek
+ * ifptex: Takayuki Yato
+ * ifpdf: Heiko Oberdiek and LaTeX3 Project
+
+
+The existing  if(u)ptex packages do far more extensive testing to
+distinguish different variants which are not copied here.
+
+A document specifically for Japanese texts may need the finer grained
+tests of the ifptex package which has tests for particular versions
+of the pTeX (Japanese TeX) variant in use, and for the mode that is
+active.
+
+This generic package only has coarser tests for the tex variant in
+use, so is sufficient for example to distinguish upTeX from pTeX, and
+to distinguish both of those from LuaTeX.
+