Introduction Attributes
Attributes describe the properties of the elements, therefore each attribute cannot appear more than once for each element. Attributes can be written in any order and separator characters (space, tab, newline) before or after the attributes or their values are ignored.

Some attributes are required (for example, the x, y, z atom coordinates), some are optional (for example the atom mass) and default values are used when they are not explicitely indicated. What are these default values and how to change them is the subject of the Gamgi part of this manual.

Some optional attributes are coupled (for example, the red, green, blue atom colors), which means that, if present, the whole set must be indicated.

Some attributes are incompatible because they describe properties that cannot be valid simultaneously for the same object (for example, a cell element cannot have simultaneously n1, n2, n3 number of cells and a volume set to sphere).

For each GAMGI object, a description of all the accepted attributes, with their possible values and restrictions, is presented in the corresponding chapter of this manual.

### Good:

    <atom element="H" x="0.0" y="0.0" z="0.0"/> all required attributes are present

    <atom
          z=  "0.0"
          y="  0.0"
          x="0.0  "
          element="H" /> equivalent to example above

    <atom element="H" x="0.0" y="0.0" z="0.0" mass="2.0"/> optional attributes may be added

### Bad:

    <atom element="H" x="0.0" z="0.0"/> a required parameter is missing

    <atom element="H" x="0.0" y="0.0" z="0.0" red="1.0" blue="1.0" /> a coupled parameter is missing

    <atom element="H" x="0.0" y="0.0" z="0.0" element="H"/> the same attribute appears twice

    <cell system="c" lattice="P" a="1.0" n1="1" n2="1" n3="1" volume="sphere" v1="1.0"/>
    incompatible attributes

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