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## org.apache.fop.fo.expr
Interface Function

All Known Implementing Classes:
  AbsFunction, BodyStartFunction, FromNearestSpecifiedValueFunction, FromParentFunction, FromTableColumnFunction, FunctionBase, InheritedPropFunction, LabelEndFunction, MaxFunction, MinFunction, ProportionalColumnWidthFunction

    public interface Function

Interface for managing XSL-FO Functions

Method Summary
`Property` | `eval(Property[] args, PropertyInfo pi)` Evaluate the function
`Property` | `getOptionalArgDefault(int index, PropertyInfo pi)`
`int` | `getOptionalArgsCount()`
`PercentBase` | `getPercentBase()`
`int` | `getRequiredArgsCount()`
`boolean` | `hasVariableArgs()` Determine if function allows variable arguments.

Method Detail

### getRequiredArgsCount

    int getRequiredArgsCount()

  Returns:
    the number of required (non-optional) arguments that must be specified in the argument list

### getOptionalArgsCount

    int getOptionalArgsCount()

  Returns:
    the number of non-required (optional) arguments that may be specified in the argument list, which, if specified, must follow the required arguments

### getOptionalArgDefault

    Property getOptionalArgDefault(int index,
                                   PropertyInfo pi)
                                   throws PropertyException

  Parameters:
    `index` - of optional argument
    `pi` - property information instance that applies to property being evaluated
  Returns:
    the default property value for the optional argument at INDEX, where INDEX is with respect to optional arguments; i.e., the first optional argument position is index 0; if no default for a given index, then null is returned
  Throws:
    `PropertyException` - if index is greater than or equal to optional args count

### hasVariableArgs

    boolean hasVariableArgs()

  Determine if function allows variable arguments. If it does, then they must appear after required and optional arguments, and all optional arguments must be specified.

  Returns:
    true if function permits additional variable number of arguments after required and (completely specified) optional arguments

### getPercentBase

    PercentBase getPercentBase()

  Returns:
    the basis for percentage calculations

### eval

    Property eval(Property[] args,
                  PropertyInfo pi)
                  throws PropertyException

  Evaluate the function

  Parameters:
    `args` - an array of Properties that should be evaluated
    `pi` - property information instance that applies to property being evaluated
  Returns:
    the Property satisfying the function
  Throws:
    `PropertyException` - for problems when evaluating the function

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