Esentially it lets the user load an ESIS file and then to write tcl commands to search, translate, analyse the parsed data. One way forward may be to add a command line option, but this is for later. Tags may also have attributes. CoST regards tags as nodes in a tree with optional attributes. This is part of the ESIS stream.
X represents an X node which can contain other nodes.
When it loads a file it stores it as a tree and every tag creates a node. If newlines are precisely important for you other than simply as whitespace you'll have to explore this carefully. CoST stores REs as nodes and this may take some getting used to. Every node has an address in the parse tree and this can be used for referencing it. There is an option for switching them on in the overview so that subtrees can be located.