Filtering with exclusion lists — excluding categories safely

Note

This example introduces exclusion-based filtering. Use this pattern only when the rule scope is intentionally broad.

Sometimes a rule should apply to almost everything, except a few specific categories.

In those cases, using an exclusion list is clearer and safer than trying to list everything you do want.

(
  /* Category Exclusion */
  $CategoryExclusion := ["OST_Doors", "OST_Windows"];

  $[
    type = "FamilySymbol"
    and $not(values.category.label in $CategoryExclusion)
  ].{
    "id": id,
    "type": type,
    "name": name,
    "assemblyCode": values.assemblyCode
  }
)

---

What this filter does (plain language)

“Select all FamilySymbols except those that belong to the Doors or Windows categories.”

Everything else is included.

---

Breaking down the new parts

1. Exclusion list

$CategoryExclusion := ["OST_Doors", "OST_Windows"];

This list defines:

“These categories must be ignored by this rule.”

Use exclusion lists when:

• The number of excluded categories is small
• The allowed scope is broad or evolving

---

2. Negation using $not(...)

$not(values.category.label in $CategoryExclusion)

This means:

• First check whether the category is in the exclusion list
• Then invert the result

So:

• If the category is in the list → excluded
• If the category is not in the list → included

---

Why $not() is used instead of !=

You might be tempted to write:

values.category.label != "OST_Doors"

This is wrong when:

• You need to exclude multiple categories
• More categories may be added later

$not(... in ...):

• Scales cleanly
• Is explicit
• Avoids chained and conditions

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Inclusion vs exclusion — when to use which

Situation	Use
Small, fixed set of allowed categories	Inclusion list
Broad scope, few categories to ignore	Exclusion list
Rule tied to a specific discipline	Inclusion
Generic or cross-discipline rule	Exclusion

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Common mistakes to avoid

Forgetting $not()

values.category.label in $CategoryExclusion

❌ This does the opposite of what you want.

---

Negating the wrong part

$not(values.category.label) in $CategoryExclusion

❌ Syntax error and incorrect logic.

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Mixing inclusion and exclusion in one filter

values.category.label in $Include and $not(values.category.label in $Exclude)

⚠️ Possible, but error-prone. Avoid unless necessary and well-documented.

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Important caution

Exclusion filters are powerful and dangerous.

If a new category is introduced in the model:

• It will automatically be included
• Possibly without you realising

Use exclusion lists only when this behaviour is intentional.

---

Rule of thumb

Inclusion defines intent. Exclusion defines exceptions.

Choose based on which is clearer for the rule’s purpose.

---

Common exclusion: Detail Items

One category that is frequently excluded by default is OST_DetailComponents (Detail Items in the Revit UI).

Despite having category.type = “Model”, Detail Items carry no model parameters and always fail generic parameter checks — causing false positives.

For the full explanation, see Detail Items and False Positives.