diff --git a/app/preproc/PdePreprocessor.java b/app/preproc/PdePreprocessor.java
index c598ae309..94b2455a0 100644
--- a/app/preproc/PdePreprocessor.java
+++ b/app/preproc/PdePreprocessor.java
@@ -39,6 +39,98 @@ import antlr.collections.impl.*;
 import com.oroinc.text.regex.*;
 
 
+/**
+ * Class that orchestrates preprocessing p5 syntax into straight Java.
+ * <P/>
+ * The PDE Preprocessor is based on the Java Grammar that comes with
+ * ANTLR 2.7.2.  Moving it forward to a new version of the grammar
+ * shouldn't be too difficult.
+ * <P/>
+ * Here's some info about the various files in this directory:
+ * <P/>
+ * <TT>java.g:</TT> this is the ANTLR grammar for Java 1.3/1.4 from the
+ * ANTLR distribution.  It is in the public domain.  The only change to
+ * this file from the original this file is the uncommenting of the
+ * clauses required to support assert().
+ * <P/>
+ * <TT>java.tree.g:</TT> this describes the Abstract Syntax Tree (AST)
+ * generated by java.g.  It is only here as a reference for coders hacking
+ * on the preprocessor, it is not built or used at all.  Note that pde.g
+ * overrides some of the java.g rules so that in PDE ASTs, there are a
+ * few minor differences.  Also in the public domain.
+ * <P/>
+ * <TT>pde.g:</TT> this is the grammar and lexer for the PDE language
+ * itself. It subclasses the java.g grammar and lexer.  There are a couple
+ * of overrides to java.g that I hope to convince the ANTLR folks to fold
+ * back into their grammar, but most of this file is highly specific to
+ * PDE itself.
+ * <TT>PdeEmitter.java:</TT> this class traverses the AST generated by
+ * the PDE Recognizer, and emits it as Java code, doing any necessary
+ * transformations along the way.  It is based on JavaEmitter.java,
+ * available from antlr.org, written by Andy Tripp <atripp@comcast.net>,
+ * who has given permission for it to be distributed under the GPL.
+ * <P/>
+ * <TT>ExtendedCommonASTWithHiddenTokens.java:</TT> this adds a necessary
+ * initialize() method, as well as a number of methods to allow for XML
+ * serialization of the parse tree in a such a way that the hidden tokens
+ * are visible.  Much of the code is taken from the original
+ * CommonASTWithHiddenTokens class.  I hope to convince the ANTLR folks
+ * to fold these changes back into that class so that this file will be
+ * unnecessary.
+ * <P/>
+ * <TT>TokenStreamCopyingHiddenTokenFilter.java:</TT> this class provides
+ * TokenStreamHiddenTokenFilters with the concept of tokens which can be
+ * copied so that they are seen by both the hidden token stream as well
+ * as the parser itself.  This is useful when one wants to use an
+ * existing parser (like the Java parser included with ANTLR) that throws
+ * away some tokens to create a parse tree which can be used to spit out
+ * a copy of the code with only minor modifications.  Partially derived
+ * from ANTLR code.  I hope to convince the ANTLR folks to fold this
+ * functionality back into ANTLR proper as well.
+ * <P/>
+ * <TT>whitespace_test.pde:</TT> a torture test to ensure that the
+ * preprocessor is correctly preserving whitespace, comments, and other
+ * hidden tokens correctly.  See the comments in the code for details about
+ * how to run the test.
+ * <P/>
+ * All other files in this directory are generated at build time by ANTLR
+ * itself.  The ANTLR manual goes into a fair amount of detail about the
+ * what each type of file is for.
+ * <P/>
+ * <B>Current Preprocessor Subsitutions:</B>
+ * <UL>
+ * <LI><TT>compiler.substitute_floats</TT> (currently "substitute_f")
+ * treat doubles as floats, i.e. 12.3 becomes 12.3f so that people
+ * don't have to add f after their numbers all the time. this is
+ * confusing for beginners.
+ * <LI><TT>compiler.enhanced_casting</TT> byte(), char(), int(), float()
+ * works for casting. this is basic in the current implementation, but
+ * should be expanded as described above. color() works similarly to int(),
+ * however there is also a *function* called color(r, g, b) in p5.
+ * will this cause trouble?
+ * <LI><TT>compiler.color_datattype</TT> 'color' is aliased to 'int'
+ * as a datatype to represent ARGB packed into a single int, commonly
+ * used in p5 for pixels[] and other color operations. this is just a
+ * search/replace type thing, and it can be used interchangeably with int.
+ * <LI><TT>compiler.web_colors</TT> (currently "inline_web_colors")
+ * color c = #cc0080; should unpack to 0xffcc0080 (the ff at the top is
+ * so that the color is opaque), which is just an int.
+ * </UL>
+ * <B>Other preprocessor functionality</B>
+ * <UL>
+ * <LI>detects what 'mode' the program is in: static (no function
+ * brackets at all, just assumes everything is in draw), active
+ * (setup plus draw or loop), and java mode (full java support).
+ * http://processing.org/reference/environment/
+ * <LI>size and background are pulled from draw mode programs and
+ * placed into setup(). this has a problem if size() is based on a
+ * variable, which we try to avoid people doing, but would like to be
+ * able to support it (perhaps by requiring the size() to be final?)
+ * <LI>currently does a godawful scrambling of the comments so that
+ * the substitution doesn't try to run on them. this also causes lots
+ * of bizarro bugs.
+ * </UL>
+ */
 public class PdePreprocessor {
 
   static final int JDK11 = 0;