Filters are a useful way to group associated levels for the purposes of viewing or not viewing as a group. For example, you might have a DGN file with several hundred levels. Within these levels could be filters for different disciplines such as Civil, Architectural, and Mechanical. Within Civil there might be levels for Civil-Existing, Civil-Proposed, Civil-Annotation, etc. You could easily define a filter called Civil that would show only levels that had the word Civil as part of the description.

Filters can be named, saved, and recalled as needed or defined on the fly for immediate one-time viewing using the Filter Row in the Level Manager dialog. Filters can be turned on or off using the Level Display dialog. Filters can be used to turn on or off levels across a model and all of its attached models. Levels can be filtered by a number of attributes such as filename, color, style, line weight, and level groups, to name a few.

Filters use different expression types depending on the column in which the expression is input. There are three basic forms of expressions: string, integer and Boolean. A syntax is provided to filter attributes with wildcards (i.e., *, ?) similar to Windows^® Explorer search criteria. In addition, set based operations such as | (or), & (and) , and – (minus) have been added. String expressions are applied to string values. Integer and Boolean values use integer and Boolean expressions. A short description of each follows:

• The string expression format is similar to the format supported in the Windows Explorer's Search dialog. In addition, set based operations such as | (or), & (and) , and – (minus) have been added. String expressions are valid for the Name, Description, File, and Logical columns in the Level Manager dialog. The following table shows examples of string expressions.

  String Expression	Matches String(s)
  lev	with the substring “lev”
  “lev”	“lev” (exactly)
  *1	ending with “1”
  lev*	starting with “lev”
  1 | 2	with the character “1” or “2”
  1 & 2	with the characters “1” and “2”
  1 – 2	with the character “1” but not “2”
  *1 | *2 | *3	ending with “1”, “2”, or “3”
  ((1 | 2) – 3)	with the character “1” or “2”, but not the character “3”
  “level 1” | “level 2”	“level 1” or “level 2” (exactly)

  Note: In the next-to-last sample string expression above, notice the use of “(” and “)” to combine the set operators.
  Note: The above string expression format is also applicable at other places such as for filtering model names in the Save As V8 Options dialog, Filter tab.
• Integer expressions are applied to integer numbers. For example, 1, 10, 15–20. The comparison operators >, >=, <, <=, and != are also supported on integer expressions. Integer expressions are valid for the Number, Color, Style, Weight and Elements in the Level Manager dialog. The following table shows examples of integer expressions.

  Integer Expression	Matches Integer Value(s)
  1,10	1 and 10
  10, 15–20	10, 15, 16, 17, 18, 19, and 20
  <20	less than 20
  >20	greater than 20
  <=20	less than or equal to 20
  >=20	greater than or equal to 20
  !=20	not equal to 20

• Boolean expressions are applied to check boxes. Boolean expressions can take a value of 0 or 1. Boolean expressions are valid for the Global, Lock, Used, and Library in the Level Manager dialog. The following table shows Boolean expressions.

  Boolean Expression	Matches Boolean Value
  0	off
  1	on