Legacy eZDataType::fromString() is not documented. Most datatypes do store the data received in this method, but not all. This leads to inconsistent behaviour in eZContentFunctions::updateAndPublishObject(), where content is not stored for some types:

• eZUserType::fromString() lacks a setContent() call.
• eZMatrixType::fromString() also does not store content.
• eZMultiOption2Type doesn't implement fromString, so it falls back on the eZDataType implentation which does nothing.

There may be more cases, I have not checked all. All datatypes should behave consistently here.