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32.19.3 Text Property Search Functions

In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.

Here are functions you can use to do this. They use eq for comparing property values. In all cases, object defaults to the current buffer.

For high performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.

These functions do not move point; instead, they return a position (or nil). Remember that a position is always between two characters; the position returned by these functions is between two characters with different properties.

— Function: next-property-change pos &optional object limit

The function scans the text forward from position pos in the string or buffer object till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos.

If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-property-change returns limit.

The value is nil if the properties remain unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos.

Here is an example of how to scan the buffer by chunks of text within which all properties are constant: 

          (while (not (eobp))
            (let ((plist (text-properties-at (point)))
                  (next-change
                   (or (next-property-change (point) (current-buffer))
                       (point-max))))
              Process text from point to next-change...
              (goto-char next-change)))
— Function: next-single-property-change pos prop &optional object limit

The function scans the text forward from position pos in the string or buffer object till it finds a change in the prop property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.

If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-single-property-change returns limit.

The value is nil if the property remains unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.

— Function: previous-property-change pos &optional object limit

This is like next-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

— Function: previous-single-property-change pos prop &optional object limit

This is like next-single-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

— Function: next-char-property-change pos &optional limit

This is like next-property-change except that it considers overlay properties as well as text properties, and if no change is found before the end of the buffer, it returns the maximum buffer position rather than nil (in this sense, it resembles the corresponding overlay function next-overlay-change, rather than next-property-change). There is no object operand because this function operates only on the current buffer. It returns the next address at which either kind of property changes.

— Function: previous-char-property-change pos &optional limit

This is like next-char-property-change, but scans back from pos instead of forward, and returns the minimum buffer position if no change is found.

— Function: next-single-char-property-change pos prop &optional object limit

This is like next-single-property-change except that it considers overlay properties as well as text properties, and if no change is found before the end of the object, it returns the maximum valid position in object rather than nil. Unlike next-char-property-change, this function does have an object operand; if object is not a buffer, only text-properties are considered.

— Function: previous-single-char-property-change pos prop &optional object limit

This is like next-single-char-property-change, but scans back from pos instead of forward, and returns the minimum valid position in object if no change is found.

— Function: text-property-any start end prop value &optional object

This function returns non-nil if at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returns nil.

The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.

— Function: text-property-not-all start end prop value &optional object

This function returns non-nil if at least one character between start and end does not have a property prop with value value. More precisely, it returns the position of the first such character. Otherwise, it returns nil.

The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.