# `ExGram.Router.Filters.CallbackQuery`
[🔗](https://github.com/rockneurotiko/ex_gram_router/blob/v0.1.0/lib/ex_gram/router/filters/callback_query.ex#L1)

Built-in filter that matches callback query updates (inline keyboard button presses).

## Usage

    # Match any callback query
    filter ExGram.Router.Filters.CallbackQuery
    filter :callback_query

    # Match a specific callback data string (exact match)
    filter :callback_query, "action_a"

    # Match callback data against a regex
    filter :callback_query, ~r/^page_\d+$/

    # Keyword list matchers
    filter :callback_query, prefix: "settings:"
    filter :callback_query, suffix: ":confirm"
    filter :callback_query, contains: "item"

## Options

- `nil` — matches any callback query update
- `string` — matches if the callback data equals the string exactly
- `%Regex{}` — matches if the callback data matches the regex
- `prefix: string` — matches if the callback data starts with the given prefix
- `suffix: string` — matches if the callback data ends with the given suffix
- `contains: string` — matches if the callback data contains the given substring

## Prefix propagation

When matching with a `prefix:` option, you can add `propagate: true` to
automatically strip the consumed prefix for all child scopes. Child scopes
can then match using the remainder of the callback data, without repeating
the parent's prefix.

    scope do
      filter :callback_query, prefix: "proj:", propagate: true

      scope do
        # Matches "proj:change" — the prefix is prepended automatically
        filter :callback_query, "change"
        handle &Handlers.change_project/1
      end

      scope do
        # Nested propagation: matches "proj:settings:volume"
        filter :callback_query, prefix: "settings:", propagate: true

        scope do
          filter :callback_query, "volume"
          handle &Handlers.volume/1
        end
      end
    end

The propagation works by writing the accumulated prefix into
`context.extra.__exgram_router__.text_prefix`. This only affects child
scopes — sibling scopes always receive the original context.

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*Consult [api-reference.md](api-reference.md) for complete listing*