Blocks and Attributes
What you must understand
Block definition versus block reference is the central distinction. Know BLOCK, WBLOCK, INSERT, and how a block's base point affects insertion. Understand attribute definitions (ATTDEF), attribute prompts, default and constant versus variable attributes, and how attributes attach to a block. Know ATTDEF modes (invisible, constant, verify, preset), the Attribute Editor (EATTEDIT), BATTMAN for synchronization, and ATTSYNC after redefining a block. Dynamic blocks with parameters and actions, plus block visibility states, appear in questions.
Traps that appear in questions
- Redefining a block does not automatically update existing attribute references; run ATTSYNC.
- WBLOCK writes a block definition to a new drawing file; it does not insert it.
- Constant attributes do not prompt on insertion and cannot be edited per reference.
- A block inserted on layer 0 with ByBlock properties takes the insertion layer's properties.
- Exploding a block loses attribute values unless they are converted; exploded attributes become text.
Worked example
A title block needs a project name that changes per drawing. Create an ATTDEF with tag PROJECT, prompt "Project name", and a default value. Select it with the title block geometry and run BLOCK. On INSERT, AutoCAD prompts for the project name. To change it later, double-click the block reference to open the Enhanced Attribute Editor.
Rule of thumb
If attributes are missing or misaligned after a block edit, run ATTSYNC before assuming the attribute definitions are wrong.