What do “patterns, which separately match parts of a page” and “interactions between patterns” mean?

Database System Concepts by Abraham Silberschatz, Henry F. Korth and S. Sudarshan says

Information extraction using simple patterns, which separately match parts of a page, is relatively error prone. Machine-learning techniques can perform much more sophisticated analysis, based on interactions between patterns, to minimize errors in the information extracted, while maximizing the amount of information extracted.

What do "patterns, which separately match parts of a page" and "interactions between patterns" mean respectively?