For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic state corresponding to a given buffer position. This function does that conveniently.
function syntax-ppss \&optional pos
This function returns the parser state that the parser would reach at position
pos starting from the beginning of the visible portion of the buffer. See Parser State, for a description of the parser state.
The return value is the same as if you call the low-level parsing function
parse-partial-sexp to parse from the beginning of the visible portion of the buffer to
pos (see Low-Level Parsing). However,
syntax-ppss uses caches to speed up the computation. Due to this optimization, the second value (previous complete subexpression) and sixth value (minimum parenthesis depth) in the returned parser state are not meaningful.
This function has a side effect: it adds a buffer-local entry to
before-change-functions (see Change Hooks) for
syntax-ppss-flush-cache (see below). This entry keeps the cache consistent as the buffer is modified. However, the cache might not be updated if
syntax-ppss is called while
before-change-functions is temporarily let-bound, or if the buffer is modified without running the hook, such as when using
inhibit-modification-hooks. In those cases, it is necessary to call
function syntax-ppss-flush-cache beg \&rest ignored-args
This function flushes the cache used by
syntax-ppss, starting at position
beg. The remaining arguments,
ignored-args, are ignored; this function accepts them so that it can be directly used on hooks such as
before-change-functions (see Change Hooks).