README.md in trace_eval-0.1.4 vs README.md in trace_eval-0.1.5

@@ -1,9 +1,24 @@
 # TraceEval
 
 Evaluates the Ruby expression(s) in string and prints each executing line.
 
+The standard ruby `tracer` does not display the source inside an `eval`:
+
+```
+$ ruby -rtracer foo.rb 
+#0:foo.rb:1::-: puts 1+2
+3
+#0:foo.rb:2::-: eval "puts 3+4\nputs 5+6\n"
+#0:(eval):1::-: -
+7
+#0:(eval):2::-: -
+11
+#0:foo.rb:3::-: puts 7+8
+15
+```
+
 ## Installation
 
 Add this line to your application's Gemfile:
 
 ```ruby
@@ -29,9 +44,50 @@
 b = 2
 puts a+b
 4
 => nil
 ```
+
+### Bugs
+
+If the traced eval in turn evals, the trace will be nonsense:
+
+```
+irb(main):001:0> extend TraceEval
+=> main
+irb(main):002:0> trace_eval "0+1\neval \"2+3\n4+5\n\"\n6+7\n"
+0+1
+eval "2+3
+0+1
+eval "2+3
+6+7
+=> 13
+```
+
+Nested `trace_eval` does work:
+
+```
+irb(main):001:0> extend TraceEval
+=> main
+irb(main):002:0> trace_eval "0+1\ntrace_eval \"2+3\n4+5\n\"\n6+7\n"
+0+1
+trace_eval "2+3
+2+3
+4+5
+6+7
+=> 13
+```
+
+## Concept of Operation
+
+- Save a random value in a magic variable to distinguish this eval
+  from others
+- Save an array of the lines of the eval string
+- Set a `TracePoint` for `:line` events (execute code on a new line)
+- When the trace point is activated
+  - Only proceed if the line's `path` is '(eval)'
+  - Only proceed if the magic variable matches the expected value
+  - Print the appropriate line from the array by `lineno`
 
 ## Development
 
 After checking out the repo, run `bin/setup` to install
 dependencies. Then, run `rake test` to run the tests. You can also run