Dedicated method for chart creation.

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branch : 1.8
Nodes are mutable so no need to return one.

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branch : 1.8
Dedicated unit test for write_chart.

--HG--
branch : 1.8
Use qualified namespaces.

--HG--
branch : 1.8
Use namespace constants.

--HG--
branch : 1.8
Use namespace constants.

--HG--
branch : 1.8
Use namespace constants.

--HG--
branch : 1.8
Use namespace constants.

--HG--
branch : 1.8
Use lxml if available.

--HG--
branch : 1.8