Move README files to a dedicated docs directory

The new dedicated docs directory has been introduced after a discussion
on GitHub[1].

Main issue it is addressing is the reduction of too many README files in
the project root directory. The new directory is dedicated for notes and
quick documentation files that either can't be put in the manual or wiki
pages or that relate to the php-src repository specifically and need to
live together with the source code.

Also the `docs` directory is by GitHub used for some repository
configuration files such as pull request templates, and contributing
documentation helper files that are integrated in the interface.

[1]: https://github.com/php/php-src/pull/3988

1 files changed, 139 insertions, 0 deletions

diff --git a/docs/output-api.md b/docs/output-api.md
new file mode 100644
index 0000000000..3c23c8e8de
--- /dev/null
+++ b/docs/output-api.md
@@ -0,0 +1,139 @@
+API adjustment to the old output control code:
+
+	Everything now resides beneath the php_output namespace,
+	and there's an API call for every output handler op.
+
+	Checking output control layers status:
+		// Using OG()
+		php_output_get_status();
+
+	Starting the default output handler:
+		// php_start_ob_buffer(NULL, 0, 1);
+		php_output_start_default();
+
+	Starting an user handler by zval:
+		// php_start_ob_buffer(zhandler, chunk_size, erase);
+		php_output_start_user(zhandler, chunk_size, flags);
+
+	Starting an internal handler without context:
+		// php_ob_set_internal_handler(my_php_output_handler_func_t, buffer_size, "output handler name", erase);
+		php_output_start_internal(handler_name, handler_name_len, my_php_output_handler_func_t, chunk_size, flags);
+
+	Starting an internal handler with context:
+		// not possible with old API
+		php_output_handler *h;
+		h = php_output_handler_create_internal(handler_name, handler_name_len, my_php_output_handler_context_func_t, chunk_size, flags);
+		php_output_handler_set_context(h, my_context, my_context_dtor);
+		php_output_handler_start(h);
+
+	Testing whether a certain output handler has already been started:
+		// php_ob_handler_used("output handler name");
+		php_output_handler_started(handler_name, handler_name_len);
+
+	Flushing one output buffer:
+		// php_end_ob_buffer(1, 1);
+		php_output_flush();
+
+	Flushing all output buffers:
+		// not possible with old API
+		php_output_flush_all();
+
+	Cleaning one output buffer:
+		// php_ob_end_buffer(0, 1);
+		php_output_clean();
+
+	Cleaning all output buffers:
+		// not possible with old API
+		php_output_clean_all();
+
+	Discarding one output buffer:
+		// php_ob_end_buffer(0, 0);
+		php_output_discard();
+
+	Discarding all output buffers:
+		// php_ob_end_buffers(0);
+		php_output_discard_all();
+
+	Stopping (and dropping) one output buffer:
+		// php_ob_end_buffer(1, 0)
+		php_output_end();
+
+	Stopping (and dropping) all output buffers:
+		// php_ob_end_buffers(1, 0);
+		php_output_end_all();
+
+	Retrieving output buffers contents:
+		// php_ob_get_buffer(zstring);
+		php_output_get_contents(zstring);
+
+	Retrieving output buffers length:
+		// php_ob_get_length(zlength);
+		php_output_get_length(zlength);
+
+	Retrieving output buffering level:
+		// OG(nesting_level);
+		php_output_get_level();
+
+	Issue a warning because of an output handler conflict:
+		// php_ob_init_conflict("to be started handler name", "to be tested if already started handler name");
+		php_output_handler_conflict(new_handler_name, new_handler_name_len, set_handler_name, set_handler_name_len);
+
+	Registering a conflict checking function, which will be checked prior starting the handler:
+		// not possible with old API, unless hardcoding into output.c
+		php_output_handler_conflict_register(handler_name, handler_name_len, my_php_output_handler_conflict_check_t);
+
+	Registering a reverse conflict checking function, which will be checked prior starting the specified foreign handler:
+		// not possible with old API
+		php_output_handler_reverse_conflict_register(foreign_handler_name, foreign_handler_name_len, my_php_output_handler_conflict_check_t);
+
+	Facilitating a context from within an output handler callable with ob_start():
+		// not possible with old API
+		php_output_handler_hook(PHP_OUTPUT_HANDLER_HOOK_GET_OPAQ, (void *) &custom_ctx_ptr_ptr);
+
+	Disabling of the output handler by itself:
+		//not possible with old API
+		php_output_handler_hook(PHP_OUTPUT_HANDLER_HOOK_DISABLE, NULL);
+
+	Marking an output handler immutable by itself because of irreversibility of its operation:
+		// not possible with old API
+		php_output_handler_hook(PHP_OUTPUT_HANDLER_HOOK_IMMUTABLE, NULL);
+
+	Restarting the output handler because of a CLEAN operation:
+		// not possible with old API
+		if (flags & PHP_OUTPUT_HANDLER_CLEAN) { ... }
+
+	Recognizing by the output handler itself if it gets discarded:
+		// not possible with old API
+		if ((flags & PHP_OUTPUT_HANDLER_CLEAN) && (flags & PHP_OUTPUT_HANDLER_FINAL)) { ... }
+
+
+Output handler hooks
+
+	The output handler can change its abilities at runtime. Eg. the gz handler can
+	remove the CLEANABLE and REMOVABLE bits when the first output has passed through it;
+	or handlers implemented in C to be used with ob_start() can contain a non-global
+	context:
+		PHP_OUTPUT_HANDLER_HOOK_GET_OPAQ
+			pass a void*** pointer as second arg to receive the address of a pointer
+			pointer to the opaque field of the output handler context
+		PHP_OUTPUT_HANDLER_HOOK_GET_FLAGS
+			pass a int* pointer as second arg to receive the flags set for the output handler
+		PHP_OUTPUT_HANDLER_HOOK_GET_LEVEL
+			pass a int* pointer as second arg to receive the level of this output handler
+			(starts with 0)
+		PHP_OUTPUT_HANDLER_HOOK_IMMUTABLE
+			the second arg is ignored; marks the output handler to be neither cleanable
+			nor removable
+		PHP_OUTPUT_HANDLER_HOOK_DISABLE
+			the second arg is ignored; marks the output handler as disabled
+
+
+Open questions
+
+	Should the userland API be adjusted and unified?
+
+	Many bits of the manual (and very first implementation) do not comply
+	with the behaviour of the current (to be obsoleted) code, thus should
+	the manual or the behaviour be adjusted?
+
+END