TPS40211 PWM LED driver topology
First, there are boost parts that are intended for LED drive that might be more suitable for your requirements.  Here's just one potential example, though there are many options on TI's website. There might be a better fit depending on your requirements:

http://www.ti.com/lit/ds/symlink/lp8860-q1.pdf

However, to answer the question:

Instead of typical voltage feedback, this circuit measures the current in the LED string with R6, and regulates the voltage on R6 (and therefore the current in the string.)

R13 and the compensation components form the error amp/compensation for the loop.

Q13 and D3 pull the comp pin down causing the peak current loop to program the peak current (not the LED string current, but the MOSFET switch current) to zero.  This shuts off the current when Q13 is on.

The loop response injection resistor R23 is optional, and is there to act as a signal injection point for a dynamic signal analyzer (or "bode plot" analyzer) to measure the open loop gain and phase of the system.  This allows you to optimize the compensation and phase margin of the system.