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### 9.2 Specifying Entities

Entities can be defined at any place in the chart, not only at the beginning.

Entity names can contain upper or lowercase characters, numbers, dots and underscores. They are case sensitive and must start with a letter or underscore and cannot end in a dot. If you want other characters, you have to put the entity name between quotation marks every time it is mentioned. This, however, makes litte sense: you can set the label of the entity to influence how the entity is called on the drawn chart.

It is also possible to define entities without attributes (having all attributes set to default) by typing

    entityname, ...;

It is also possible to change some of the attributes later in the chart, well after the definition of the entity. The syntax is the same as for definition — obviously the name identifies an already defined entity.

Note that typing several entity definition commands one after the other is the same as if all entity definitions were given on a single line. Thus

    a;
    b;
    c;

is equivalent to

    a, b, c;

Also, `heading` commands are combined with the definitions into a single visual line of entity headings.