This is the official manual for the latest Org-mode release.
Org syntax includes pre-defined blocks (see Paragraphs and Literal examples). It is also possible to create blocks containing raw code targeted at a specific back-ends (e.g., ‘#+BEGIN_LATEX’).
Any other block is a special block. Each export back-end decides if they should be exported, and how. When the block is ignored, its contents are still exported, as if the block were not there. For example, when exporting a ‘#+BEGIN_TEST’ block, HTML back-end wraps its contents within ‘<div name="test">’ tag. Refer to back-end specific documentation for more information.