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Reusable blocks are re2c blocks that can be reused any number of times and combined with other re2c blocks. They are defined with ``/*!rules:re2c[:<name>] ... */`` (the ``<name>`` is optional). A rules block can be used in two contexts: either in a use block, or in a use directive inside of another block. The code for a rules block is generated at every point of use. Use blocks are defined with ``/*!use:re2c[:<name>] ... */``. The ``<name>`` is optional; if not specified, the associated rules block is the most recent one (whether named or unnamed). A use block can add named definitions, configurations and rules of its own. An important use case for use blocks is a lexer that supports multiple input encodings: the same rules block is reused multiple times with encoding-specific configurations (see the example below). In-block use directive ``!use:<name>;`` can be used from inside of a re2c block. It merges the referenced block ``<name>`` into the current one. If some of the merged rules and configurations overlap with the previously defined ones, conflicts are resolved in the usual way: the earliest rule takes priority, and latest configuration overrides preceding ones. One exception are the special rules ``*``, ``$`` and (in condition mode) ``<!>``, for which a block-local definition overrides any inherited ones. Use directive allows one to combine different re2c blocks together in one block (see the example below). Named blocks and in-block use directive were added in re2c version 2.2. Since that version reusable blocks are allowed by default (no special option is needed). Before version 2.2 reuse mode was enabled with ``-r --reusable`` option. Before version 1.2 reusable blocks could not be mixed with normal blocks.