10. The method of establishing a plain text document from a HTML document as claimed in claim 1 , wherein the contents of the HTML elements identified by a specific searching method are used as the content of the target group(s) if there is no target tag in the pre-processed HTML document.
10. The method of establishing a plain text document from a HTML document as claimed in claim 1 , wherein the contents of the HTML elements identified by a specific searching method are used as the content of the target group(s) if there is no target tag in the pre-processed HTML document. 11. The method of establishing a plain text document from a HTML document as claimed in claim 10 , wherein the searching method comprises the steps of: identifying the HTML element having the longest content in the pre-processed HTML document; shifting a current HTML element to a candidate HTML element having the contents with lengths longer than a first predetermined threshold and having intervals with the longest HTML element smaller than a second predetermined threshold; repeating the shifting step for the HTML elements ahead of the longest HTML elements until there is no candidate HTML element, and identifying the final current HTML element as a base content, and repeating the shifting step for the HTML elements behind the longest HTML elements until there is no candidate HTML element, and identifying the final current HTML element as an ending HTML element; and using the contents of the starting and ending HTML elements, and those of the HTML elements between the starting and ending HTML elements as the content of the target group.