This class is used for storing a text string which has all the same font and colour attributes. The entire hypertext file is broken up into a list of these fragments, and the Compile function assigns actual font and colour attributes to each chunk. A text chunk may also mark the start of a line (each line has a special start line text chunk).
If a chunk represents the start of a block, the block_id is this block. For chunks within a block, the block_id is always the id of the block currently in scope. A text chunk which marks the end of a block has block_id set to the next block's id, but end_block set to the ending block's id. This is because a text chunk contains the next fragment of text, and an end block chunk has two purposes: to end one block, and continue another.
wxTextChunk::background_colour
wxTextChunk::special_attribute