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 good 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.
The function scans the text forward from position pos in the string or buffer object until 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, this function 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)))
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.
The function scans text for a change in the prop property, then returns the position of the change. The scan goes forward from position pos in the string or buffer object. In other words, this function 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.
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.
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.
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.
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.
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.
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.
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.
Search for the next region that has text property prop set to value according to predicate.
This function is modelled after search-forward and friends in that it moves point, but it returns a structure that describes the match instead of returning it in match-beginning and friends.
If the text property can’t be found, the function returns nil. If it’s found, point is placed at the end of the region that has this text property match, and a prop-match structure is returned.
predicate can either be t (which is a synonym for equal), nil (which means “not equal”), or a predicate that will be called with two parameters: The first is value, and the second is the value of the text property we’re inspecting.
If not-current, if point is in a region where we have a match, then skip past that and find the next instance instead.
The prop-match structure has the following accessors: prop-match-beginning (the start of the match), prop-match-end (the end of the match), and prop-match-value (the value of property at the start of the match).
In the examples below, imagine that you’re in a buffer that looks like this:
This is a bold and here's bolditalic and this is the end.
That is, the “bold” words are the bold face, and the “italic” word is in the italic face.
With point at the start:
(while (setq match (text-property-search-forward 'face 'bold t))
(push (buffer-substring (prop-match-beginning match)
(prop-match-end match))
words))
This will pick out all the words that use the bold face.
(while (setq match (text-property-search-forward 'face nil t))
(push (buffer-substring (prop-match-beginning match)
(prop-match-end match))
words))
This will pick out all the bits that have no face properties, which will result in the list ‘("This is a " "and here's " "and this is the end")’ (only reversed, since we used push).
(while (setq match (text-property-search-forward 'face nil nil))
(push (buffer-substring (prop-match-beginning match)
(prop-match-end match))
words))
This will pick out all the regions where face is set to something, but this is split up into where the properties change, so the result here will be ‘("bold" "bold" "italic")’.
For a more realistic example where you might use this, consider that you have a buffer where certain sections represent URLs, and these are tagged with shr-url.
(while (setq match (text-property-search-forward 'shr-url nil nil)) (push (prop-match-value match) urls))
This will give you a list of all those URLs.
This is just like text-property-search-backward, but searches backward instead. Point is placed at the beginning of the matched region instead of the end, though.
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Licensed under the GNU GPL license.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Property-Search.html