2. Language overview
2.1. Basic concepts
The basic concepts within SDF documents are:
| Concept | Description | 
| paragraph | one or more lines of text | 
| phrase | a section of text within a paragraph | 
| style | the type of a document, paragraph, phrase or table (e.g. H1) | 
| macro | a command embedded in a document (e.g. !define) | 
| variable | a named value (e.g. DOC_NAME) | 
| filter | a rule to use when processing certain sections of text (e.g. table) | 
| attribute | a named parameter of a paragraph, phrase or filter (e.g. jump) | 
| expression | a literal or expression to evaluate (e.g. "Ian Clatworthy"). | 
Further details about these are given below.
