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RDINFO accesses blocks of text in what computer science calls a "tree". A "tree" is simply a block of text which points to other blocks, like the root of a tree is connected to the branches. These new blocks can point to other blocks, like big branches splitting into little branches, and so on. The text blocks are called "nodes". RDINFO does not care if the branches connect to branches at other than the current level, so it actually handles "directed graphs"; all that matters is that some nodes point to others. Computer trees are conventionally written with the root at the top, like an upside-down tree, because we like to start at the top of the page and move down. A simple INFO tree might look something like this: Top | | --------------------------------------------------- | | | One Two Three | | ----------------- | | | | | One-a One-b One-c Two-a | ---------- | | Two-b Two-c The "M" (menu) command in node "Top" can take you to nodes "One", "Two", or "Three". In "One", the "M" command can then get you to nodes "One-a", "One-b", and "One-c"; in "Two", it can get you to "Two-b" and "Two-c". Node "Three" does not have a menu; it is a "leaf" node. The "U" command can take you from "Two-b" up to "Two", and another "U" gets you up to "Top". The "N" (next) command takes you from "One-a" to "One-b", another gets you to "One-c". A third might go anywhere else in the tree, but the current implementation of RDINFO automatically figures out the connections, and "One-c" is not given a "next" node. The "P" (previous) command steps in the reverse direction to "N". The "G" (go to) command can take you immediately anywhere you want to go in the INFO tree, if you know the node name. The "L" (last) command takes you back to the last node you visited, so you need not remember how you got to the current one. The nodes in the tree do not have to reside in the same text file, because node names can contain parenthesized filenames. This lets the documentation in the INFO system grow quite large and have many authors, without having to have enormous text files or worry about author conflicts and file write access problems. Usually, text relating to a single subject will be kept in one file, because it can be then easily searched with the "S" (search) and "K" (keyword) commands. Moving around the INFO tree is quite fast, because each INFO file is a direct access file with a node directory at the beginning which lets RDINFO position to any node in any order, without having to read all of the file.