ViewComponent feature analogous to Web-component slots or React children: a component declares named 'holes' (renders_one / renders_many) that callers fill with blocks or nested components. Unlike the default `content` block (only evaluated when called), slot blocks are always evaluated. Enables DSL-like usage such as `stats.with_number(...)` or `header.with_breadcrumb_item(...)`. Radoslav Stankov aliases slots (`as: :number`, `as: :action`) to make the DSL read naturally.