Strings

Strings which include spaces (for example, perhaps the units or comments attribute of a column) must be enclosed in single or double quotes. The quotes must be `matching': a string started with a single quote must be ended with a single quote and similarly for a double quote. A double quote can be included within a string terminated with single quotes and vice versa. Strings which do not include embedded spaces may optionally be enclosed in quotes, but they do not need to be.