The code was designed to have extendability, and uses a basic parsing and evaluation model. Every command has a hash that references a regular expression in the {\tt Expressions} object defined in {\tt expressions.js}, and a function in the {\tt Functions} object also defined in {\tt expressions.js} for what to do once the expression matches. 


To add new commands, you can simply add a new regular expression inside the {\tt Expressions} object, and a match function in {\tt Functions} object of the same hash name. If you defined a new command to be evaluated within a PSTricks environment, then you should also add a graphing function inside of {\tt psgraph.js}. If you want to add a new environment, then you can add a regular expression to the {\tt Delimiters} object in {\tt expressions.js} and add a new block inside of the {\tt renderer.js} file's {\tt beforeRender} method.


The parser located in {\tt parse.js} chops and dices all text into an array of lines using the newline character as the delimiter. This is a very simple model for parsing, as it enabled focus to be on the commands instead of writing a full grammar. Writing a full parser would be ideal for future versions to be able to properly parse multi-line environments that use opening braces '{' and closing braces '}' on separate lines. 


After the parser creates an array of text it passes all the lines through the defined regular expressions, first parsing any text-based expressions primarily for \TeX\ commands, and then parses more advanced expressions such as PSTricks variables and expressions as they are defined within their respective environments.


The parser instantiates and manages environments during parsing, and creates new environments packing them with state when any delimiters are detected, which are also defined as regular expressions inside of {\tt expressions.js}.


Each environment has its own execution context, and a hash of matched objects that map to \TeX\ commands. It also stores the intial settings, which can be modified during evaluation. When the match functions are called, they are given the context using the JavaScript {\tt Function.call} passing the context to be evaluated for {\tt this} object. The reason for this is to properly address coordinate transformations, which requires access to the current environment's variables and context and is at the core of the platform.
 

Certain expressions can modify the current environment variables and settings, so that during evaluation, the graphics and text can update accordingly. Some commands that modify the environment are {\tt pspicture} and {\tt psset}, because they define the size of pictures and units or dimensions. 


Expressions and Parsing