Keywords are separated by a comma. If you only have one keyword no comma is necessary. Separating keywords with a comma and space (see SPACES EXAMPLES BELOW) will return different results than not using a space after the comma.

Separation Examples:

"Pragma", "PRAGMA" and "pragma" are all handled the same.

Looking for "ragma" is different from " ragma". Basically, a space will be looked for and so any word beginning a paragraph will be ignored. With no space, only that sequence of letters are searched for anywhere in any word.

Phrases will be looked for as a single keyword and each character is significant.
"pragma 6", "pragma6" and "pragma_6" (one with space, no space and one with underline) are 3 different phrases and will be searched for EXACTLY.
"windows nt 4.5" will look for EXACTLY that phrase. While "windows nt" will be in some documents, or "nt 4.5" might be also, if "windows nt 4.5" is not in the document, it will not be pulled up.

Partial words will be looked for as a single keyword and each character is significant.
The keyword "install" will pull up "install", "installing" , "installation" and "pre-installation"
In the above example, the keyword " install" (space preceding) will not bring up "pre-installation" or if the beginning word of a paragraph is "Installing".

"Or" means any document that has ANY of the keywords.
"And" means that only documents with ALL of the keywords will be hit.