BEST "ex-ample": NIST Digital Library of Mathematical Functions; Abramowitz and Stegun’s (1964) Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables;a LaTeX to XML/mathML Converter

For 50 years, a standard reference in mathematical work has been Abramowitz and Stegun’s (1964) Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables. It has provided a marvellous collection of results and tables that have been indispensable for a generation of mathematicians.
Now it has been reissued as the NIST Handbook of Mathematical Functions (Cambridge University Press) with a free web edition called the NIST Digital Library of Mathematical Functions. It has been updated to include lots of new topics.
http://dlmf.nist.gov/
The equation is an image with latex code between alt-tags (automatic mode)
You can change this (http://dlmf.nist.gov/help/customize):

• Automatic
• XHTML+MathML
• HTML+images

You can also select the Visualization Format:

• VRML
• X3D

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See also:
A LaTeX to XML Converter:
http://dlmf.nist.gov/LaTeXML/