elisp: Examining Properties
31.19.1 Examining Text Properties
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The simplest way to examine text properties is to ask for the value of a
particular property of a particular character. For that, use
‘get-text-property’. Use ‘text-properties-at’ to get the entire
property list of a character. 
Property Search, for functions to
examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that
positions in a string start from 0, whereas positions in a buffer start
from 1.
-- Function: get-text-property pos prop &optional object
This function returns the value of the PROP property of the
character after position POS in OBJECT (a buffer or string). The
argument OBJECT is optional and defaults to the current buffer.
If there is no PROP property strictly speaking, but the character
has a property category that is a symbol, then ‘get-text-property’
returns the PROP property of that symbol.
-- Function: get-char-property position prop &optional object
This function is like ‘get-text-property’, except that it checks
overlays first and then text properties. Overlays.
The argument OBJECT may be a string, a buffer, or a window. If it
is a window, then the buffer displayed in that window is used for
text properties and overlays, but only the overlays active for that
window are considered. If OBJECT is a buffer, then overlays in
that buffer are considered first, in order of decreasing priority,
followed by the text properties. If OBJECT is a string, only text
properties are considered, since strings never have overlays.
-- Function: get-pos-property position prop &optional object
This function is like ‘get-char-property’, except that it pays
attention to properties’ stickiness and overlays’ advancement
settings instead of the property of the character at (i.e., right
after) POSITION.
-- Function: get-char-property-and-overlay position prop &optional
object
This is like ‘get-char-property’, but gives extra information about
the overlay that the property value comes from.
Its value is a cons cell whose CAR is the property value, the same
value ‘get-char-property’ would return with the same arguments.
Its CDR is the overlay in which the property was found, or ‘nil’,
if it was found as a text property or not found at all.
If POSITION is at the end of OBJECT, both the CAR and the CDR of
the value are ‘nil’.
-- Variable: char-property-alias-alist
This variable holds an alist which maps property names to a list of
alternative property names. If a character does not specify a
direct value for a property, the alternative property names are
consulted in order; the first non-‘nil’ value is used. This
variable takes precedence over ‘default-text-properties’, and
‘category’ properties take precedence over this variable.
-- Function: text-properties-at position &optional object
This function returns the entire property list of the character at
POSITION in the string or buffer OBJECT. If OBJECT is ‘nil’, it
defaults to the current buffer.
-- Variable: default-text-properties
This variable holds a property list giving default values for text
properties. Whenever a character does not specify a value for a
property, neither directly, through a category symbol, or through
‘char-property-alias-alist’, the value stored in this list is used
instead. Here is an example:
(setq default-text-properties '(foo 69)
char-property-alias-alist nil)
;; Make sure character 1 has no properties of its own.
(set-text-properties 1 2 nil)
;; What we get, when we ask, is the default value.
(get-text-property 1 'foo)
⇒ 69
Info Catalog
elisp: Text Properties
elisp: Changing Properties