I thought I would create this post to explain how Blocks work in TBC (and to a large extent in AutoCAD also).
How is Layer 0 Used in Blocks
If all the content of a Block is defined on Layer 0 (this is a unique / special case) then the entire block will be turned On and Off when the layer on which it is inserted is turned On and Off. Turning Layer 0 on and off does not affect the appearance of a block.
If any elements of a block are defined on a layer other than layer 0, then those elements will be turned On and Off when the layer on which the element inside the block is turned On and Off.
When a block is exploded, all the elements of the exploded block will be placed on the layer on which they were drawn on prior to creating the block definition used to create the blocks being exploded.
How Should You Define Blocks?
All block graphical elements should be defined on Layer 0 unless you intend to later explode the blocks for the benefit of accessing the linework etc. embedded within the block. If the block is to be left intact as a block, it will perform best if it is all drawn on layer 0.
Color Management In Blocks
Block elements can be drawn in any color.
If you set the color of an element in a block to a specific color, that element in the block will always be drawn in that color.
If you set the color of an element in a block to color “ByLayer” then the element will be drawn in the color of the layer on which the block is inserted provided the blocks color is set to “ByLayer”.
If you set the color of an element in a block to color “ByLayer” then the element will also be drawn in the color of the layer if the blocks color is set to “ByBlock / Feature”. This is because the ByBlock color in this case is ByLayer therefore it inherits the color of the layer.
However if the color of the element in the Block is set to a specific color e.g. Red, then setting the Blocks color to “ByBlock” or “ByLayer” will cause that element to be drawn in Red because you have defined a specific color for that element in the block.
Line Fills In Blocks
If a block has a closed line included in the block, and that line has the “Auto-close” property set to Yes, then you can assign the line a Fill, a Fill color and a Fill Transparency.
Fill colors are handled in the same way that line colors are handled (see above).
Fill colors and hatch patterns are handled in the same way.
Text Items In A Block
Text can be inserted into a block, but at this time the text cannot really be smart text i.e. it cannot determine the N, E, Elev, Station. Offset etc. values from its own insertion point.
Text Color is handled the same way as line color is handled.
Exploding a Block
When you explode a block, the component elements will be exploded out onto the layers on which they were drawn before creating the block definition i.e. if you drew them all on Layer 0 then the lines and text and hatches / fills will all end up on layer 0 after an explode.
Editing a Block
If you select an instance of a block and right click it, you can select New Block Edit View to edit the blocks definition. Any changes that you make to the block definition will instantly be reflected in all instances of the block placed in the project.
You can edit an individual blocks properties using the Properties Pane to change its position, elevation, color definition etc.