The main purpose of the software here is to create and work over annotations of the selected articles. The form of annotation used is the standoff annotation. Where a dictionary term such as "yellow fever" is found in the text, the passage is analysed as
- (preceding phrase) yellow fever (following phrase)
and the two phrases are stored, separately from the text.
The place in the text before the "y" of "yellow fever" is the anchor point" of the annotation. It is assigned a number, the offset. The offset notionally counts the length of the whole preceding text, back to the start of the article. Because that concept is a bit vague, it means in practice the length (number of characters, including spaces) in the preceding text, calculated from a definite simplified version.
The major kinds of items in this Wikibase site are annotations, anchor points and article items. The article items are a subclass of anchor points, and are different from the pages with actual article text. They can be thought of hooks created for each actual article, on which data about the article can be hung. As anchor points, they are considered as standing right at the start of the text: their offset is 0.