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### Data structures
+To become data extraction Zen Masters, we first need to understand the data
+structure returned by Nokogiri. Nokogiri converts HTML and XML documents in
+to a tree data structure.
+
+For example, an HTML document that looks like this:
+
+
+
+ Hello!
+
+
+ Hello World!
+
+
+
+will be represented in memory with a tree that looks like this:
+
+
+
## Data Extraction
### Basic XPath