Every characteristic is inherited unless it is explicitly specified not to be in this International Standard. For each inherited characteristic, there is an expression in this International Standard specifying the initial value for that characteristic. Each non-inherited characteristic has a default value.

While a construct-expression is being evaluated, a current overriding style is in effect. When the processing of a node starts, the current overriding style is empty. The next-match procedure can change the current overriding style during the evaluation of a construct-expression. That construct-expression may, in turn, call next-match to change the current overriding style, and so on.

The expression specifying an inherited characteristic c for a flow object is determined when the make-expression is evaluated using the first of the following rules that is applicable:

• If a keyword of force! c : was specified, then the corresponding expression shall be used.
• If the current overriding style contains an expression for c , then that expression shall be used.
• If a keyword of c : was specified, then the corresponding expression shall be used.
• If use: was specified on the flow object, and the corresponding style object specifies an expression for c , then that expression shall be used.
• Otherwise, an expression (inherited- c ) shall be used.

The set of characteristics and corresponding expressions for a style object is determined in a similar manner during the evaluation of the style-expression. For each inherited characteristic c , the expression that the style object has for c is determined using the first of the following rules that is applicable:

• If a keyword of force! c : was specified, then the corresponding expression shall be used.
• If the current overriding style contains an expression for c , then that expression shall be used.
• If a keyword of c : was specified, then the corresponding expression shall be used.
• If use: was specified on the flow object, and the corresponding style object specifies an expression for c , then that expression shall be used.

If none of these rules are applicable, then the style object contains no expression for c .

For each non-inherited characteristic c applicable to some flow object, if the make-expression for that flow object specifies the c : keyword, then the corresponding expression shall be evaluated and used; otherwise, the default for that characteristic shall be determined as specified for that characteristic and flow object class.

The expression specifying the value of a characteristic in a make-expression or style-expression shall not be evaluated immediately; instead the expression shall be associated with the characteristic in the created flow object or style object. The values of the free variables in the expression are remembered and are used when the expression is evaluated, as with a lambda expression. The current node is also remembered and restored for the evaluation of the expression.

When the flow object tree has been sufficiently constructed so that the position of a flow object in the flow object tree has been determined, then the expressions specifying the values for the characteristics applicable to that flow object shall be evaluated.

An expression specifying the value of a characteristic shall be evaluated with respect to two flow objects, which are referred to as the value flow object and the specification flow object. The value of a characteristic for a flow object is determined by evaluating the expression specifying that characteristic with both the value flow object and the specification flow object equal to that flow object.

For any inherited characteristic, c , there is a procedure inherited- c . This procedure shall be used only in the evaluation of an expression specifying a value for a characteristic. The procedure returns the result of evaluating the expression that specifies c for the flow parent of the specification flow object; this expression is evaluated with the value flow object unchanged and with the specification flow object equal to the flow parent of the current specification flow object. If the current specification flow object has no flow parent because it occurs as a characteristic value of some flow object, then that flow object shall be treated as the flow parent for this purpose. If the current specification flow object has no flow parent because it is used in a generate-specification or a decoration-specification, then the page-sequence or column-set-sequence flow object that is using the page-model or column-set-model in which that generate-specification or decoration-specification occurs shall be treated as the flow parent for this purpose. Otherwise, if the current specification flow object has no flow parent then inherited- c returns the result of evaluating the expression specifying the initial value of c ; there is no specification flow object during the evaluation of this specification, and it shall be an error if it calls inherited- c for any inherited characteristic c .

The procedure inherited- c behaves differently when:

• the flow parent of the specification flow object is a table or a table-part;
• the value flow object is a table-cell of that table or table-part or is in a table-cell of that table or table-part; and
• the table or table-part contains a table-column flow object that specifies c and has the same column number as that table-cell.

In this case, inherited- c shall return the result of evaluating the specification of c in the table-column; this expression shall be evaluated with the value flow object unchanged and with the specification flow object equal to the table flow object.

For each inherited characteristic c , actual- c shall return the value of c for the value flow object. This procedure shall be used only in the evaluation of an expression specifying a value for a characteristic. It shall be an error to call actual- c with a value flow object of f in the course of determining the value of c for f . Use of this procedure requires the actual-characteristic feature.

This procedure shall be used only in the evaluation of an expression specifying a value for an inherited characteristic. There shall be an odd number of arguments. All arguments other than the last shall be interpreted as a series of pairs, where the first member of the pair is a string specifying a public identifier, and the second member is any object. If the value flow object is not a character flow object or is a character flow object that has a script property that is not #f, then char-script-case shall return its last argument. Otherwise, the value of the script characteristic shall be compared in turn against the first member of each argument pair; if it matches, then the second member shall be returned; if there is no match, then the last argument shall be returned.

This declares identifier to be an additional inherited characteristic. It also has the effect of declaring procedures inherited- identifier and actual- identifier . The string is a public identifier specifying the semantics of the characteristic. If an implementation does not recognize the specified public identifier, it shall ignore uses of the characteristic. The expression is the specification of the initial value of the characteristic.

This declares identifier to be an additional non-inherited characteristic of a character flow object and also declares identifier to be an additional character property. The string shall be a public identifier specifying the semantics of the characteristic. The default value of the characteristic is the value of the identifier property of the character that is the value of the char: characteristic of the flow object. The default value of the property is the value of expression. This expression shall be evaluated normally; it shall not be evaluated in the special way that the values of characteristics are evaluated, nor shall it be evaluated with respect to a current node.

This declares the initial value of the inherited characteristic identifier to be an expression. This shall not be used for characteristics declared with an application-characteristic-declaration.