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+########
+Overview
+########
+
+.. default-domain:: cpp
+.. highlight:: cpp
+.. namespace:: exess
+
+The complete API is declared in ``exess.hpp``:
+
+.. code-block:: cpp
+
+   #include <exess/exess.hpp>
+
+**************
+Reading Values
+**************
+
+Each supported type has a read function that takes a pointer to an output value,
+and a string to read.
+It reads the value after skipping any leading whitespace,
+then returns an :struct:`ExessResult` with a ``status`` code and the ``count`` of characters read.
+For example:
+
+.. code-block:: cpp
+
+   int32_t     value = 0;
+   ExessResult r     = exess_read_int(&value, "1234");
+   if (!r.status) {
+     fprintf(stderr, "Read %zu bytes as int %d\n", r.count, value);
+   }
+
+If there was a syntax error,
+the status code indicates the specific problem.
+If a value was read but didn't end at whitespace or the end of the string,
+the status :enumerator:`EXESS_EXPECTED_END` is returned.
+This indicates that there is trailing garbage in the string,
+so the parse may not be complete or correct depending on the context.
+
+**************
+Writing Values
+**************
+
+The corresponding write function takes a value to write,
+a buffer size in bytes, and a buffer to write to.
+It returns an :struct:`ExessResult`,
+with a ``status`` code and the ``count`` of characters written,
+not including the trailing null byte.
+
+For datatypes with a bounded length,
+the `constexpr` function template :func:`max_length` returns the maximum length of the canonical representation of any value.
+This can be used to allocate buffers statically or on the stack,
+for example:
+
+.. code-block:: cpp
+
+   char buf[exess::max_length<int>() + 1] = {0};
+
+   exess::Result r = exess::write(1234, sizeof(buf), buf);
+   if (r.status != exess::Status::success) {
+     std::cerr << "Write error: " << exess::strerror(r.status) << "\n";
+   }
+
+******************
+Allocating Strings
+******************
+
+Exess doesn't do any allocation itself,
+so the calling code is responsible for providing a large enough buffer for output.
+The `count` returned by write functions can be used to determine the space required for a specific value.
+If the write function is called with a null output buffer,
+then this count is still returned as if a value were written.
+This can be used to precisely allocate memory for the string,
+taking care to allocate an extra byte for the null terminator.
+For example:
+
+.. code-block:: cpp
+
+   exess::Result r   = exess::write(1234, 0, NULL);
+   char*         str = (char*)calloc(r.count + 1, 1);
+
+   r = exess_write_int(1234, r.count + 1, buf);
+
+Note that for some types,
+this operation can be about as expensive as actually writing the value.
+For example, it requires binary to decimal conversion for floating point numbers.
+For ``float`` and ``double``,
+since the length is bounded and relatively small,
+it may be better to write immediately to a static buffer,
+then copy the result to the final destination.
+
+********
+Variants
+********
+
+The fundamental read and write functions all have similar semantics,
+but different type signatures since they use different value types.
+:struct:`ExessVariant` is a tagged union that can hold any supported value,
+allowing generic code to work with values of any type.
+
+Any value can be read with :func:`exess_read_variant` and written with :func:`exess_write_variant`,
+which work similarly to the fundamental read and write functions,
+except the read function takes an additional ``datatype`` parameter.
+The expected datatype must be provided,
+attempting to infer a datatype from the string content is not supported.
+
+Datatypes
+=========
+
+:enum:`ExessDatatype` enumerates all of the supported variant datatypes.
+The special value :enumerator:`EXESS_NOTHING` is used as a sentinel for unknown datatypes or other errors.
+
+If you have a datatype URI, then :func:`exess_datatype_from_uri()` can be used
+to map it to a datatype.  If the URI is not for a supported datatype, then it will return :enumerator:`EXESS_NOTHING`.
+
+Unbounded Numeric Types
+=======================
+
+There are 6 unbounded numeric types:
+decimal, integer, nonPositiveInteger, negativeInteger, nonNegativeInteger, and positiveInteger.
+:struct:`ExessVariant` supports reading and writing these types,
+but stores them in the largest corresponding native type:
+``double``, ``int64_t``, or ``uint64_t``.
+If the value doesn't fit in this type,
+then :func:`exess_read_variant` will return an :enumerator:`EXESS_OUT_OF_RANGE` error.
+
+Writing Canonical Form
+======================
+
+Since values are always written in canonical form,
+:struct:`ExessVariant` can be used as a generic mechanism to convert any string to canonical form:
+simply read a value,
+then write it.
+If the value itself isn't required,
+then :func:`exess_write_canonical` can be used to do this in a single step.
+For example, this will print ``123``:
+
+.. code-block:: cpp
+
+   char buf[4] = {0};
+
+   ExessResult r = exess_write_canonical(" +123", EXESS_INT, sizeof(buf), buf);
+   if (!r) {
+     printf("%s\n", buf);
+   }
+
+Note that it is better to use :func:`exess_write_canonical` if the value isn't required,
+since it supports transforming some values outside the range of :struct:`ExessVariant`.
+Specifically,
+decimal and integer strings will be transformed directly,
+avoiding conversion into values and the limits of the machine's numeric types.