Notable changes between the WIP draft and the v1 specification are:

• Specify error types
• Clarify return values of expressions that encounter errors
• Clarify that missing attributes result in an error and the expression
  returning it's default value
• Add support for boolean to integer and integer to boolean type casting
• Clarify the order of operations
• Clarify how user defined functions work
• Define the default "zero" values for the built in types
• Clarify that string comparisons are case sensitive
• Specify which characters are treated as whitespace for the TRIM function
• Specify that functions must still return values along with errors, as well as
  the behaviour when user defined function do not do this correctly
• For the fail fast error handling mode, expressions now return the zero value
  for their return type when they encounter an error, rather than undefined