symfony/symfony-docs — comment on commit 78fbe0505f42b091eca4dd42b780291e3eed950d
File: cookbook/form/create_custom_field_type.rst line 85
By stof:

the name is the key to access the form type, be it in the rendering (to find the needed block), in the inheritance tree (``getParent`` returns the name of the parent) or when adding a field in the builder (you could of course create a new instance each time but this is useless as the form factory reuses the same instance, and it would be painful when having dependencies)