roy, thanks for help ! my intention is adds text to block definition.
I would not pursue this if I were you. There are quite a lot of issues to solve and the result will never be a very user-friendly application. Using the block editor (or refedit) will be more convenient.
Some of the issues involved:
1.
Order of the selected text entities and order of existing attdefs.
2.
Translating entities from current drawing space (MS or PS) to block space.
3.
Prompting the user for multiple string values which can be confusing.
4.
Updating existing block references.
But if you really want to do this, using Visual Lisp is probably better (look at the AddAttribute method).