Revert of Updating OTS repo from https://github.com/khaledhosny/ots.git

third_party/ots/docs/DesignDoc.md

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-What's OTS?
-===========
-
-Sanitiser for OpenType (OTS) is a small library which parses OpenType files
-(usually from `@font-face`) and attempts to validate and sanitise them. This
-library is primarily intended to be used with Chromium. We hope this reduces
-the attack surface of the system font libraries.
-
-What the sanitiser does is as follows:
-
-1. Parses an original font. If the parsing fails, OTS rejects the original
-   font.
-2. Validates the parsed data structure. If the validation fails, it rejects the
-   original font as well.
-3. Creates a new font on memory by serializing the data structure, and we call
-   this "transcoding".
-
-By transcoding fonts in this way, it is ensured that:
-
-1. All information in an original font that OTS doesn't know or can't parse is
-   dropped from the transcoded font.
-2. All information in the transcoded font is valid (standard compliant).
-   Particularly 'length' and 'offset' values, that are often used as attack
-   vectors, are ensured to be correct.
-
-Supported OpenType tables
-=========================
-
-| Name   | Mandatory table?            | Supported by OTS? | Note   |
-|--------|-----------------------------|-------------------|--------|
-| `sfnt` | Yes                         | Yes               | Overlapped tables are not allowed; it is treated as a fatal parser error.|
-| `maxp` | Yes                         | Yes               |        |
-| `head` | Yes                         | Yes               |        |
-| `hhea` | Yes                         | Yes               |        |
-| `hmtx` | Yes                         | Yes               |        |
-| `name` | Yes                         | Yes               |        |
-| `OS/2` | Yes                         | Yes               |        |
-| `post` | Yes                         | Yes               |        |
-| `cmap` | Yes                         | Partialy          | see below |
-| `glyf` | Yes, for TrueType fonts     | Yes               | TrueType bytecode is supported, but OTS does **not** validate it.|
-| `loca` | Yes, when glyf table exists | Yes               |        |
-| `CFF ` | Yes, for OpenType fonts     | Yes               | OpenType bytecode is also supported, and OTS **does** validate it.|
-| `cvt ` | No                          | Yes               | Though this table is not mandatory, OTS can't drop the table from a transcoded font since it might be referred from other hinting-related tables. Errors on this table should be treated as fatal.|
-| `fpgm` | No                          | Yes               | Ditto. |
-| `prep` | No                          | Yes               | Ditto. |
-| `VDMX` | No                          | Yes               | This table is important for calculating the correct line spacing, at least on Chromium Windows and Chromium Linux.|
-| `hdmx` | No                          | Yes               |        |
-| `gasp` | No                          | Yes               |        |
-| `VORG` | No                          | Yes               |        |
-| `LTSH` | No                          | Yes               |        |
-| `kern` | No                          | Yes               |        |
-| `GDEF` | No                          | Yes               |        |
-| `GSUB` | No                          | Yes               |        |
-| `GPOS` | No                          | Yes               |        |
-| `morx` | No                          | No                |        |
-| `jstf` | No                          | No                |        |
-| `vmtx` | No                          | Yes               |        |
-| `vhea` | No                          | Yes               |        |
-| `EBDT` | No                          | No                | We don't support embedded bitmap strikes.|
-| `EBLC` | No                          | No                | Ditto. |
-| `EBSC` | No                          | No                | Ditto. |
-| `bdat` | No                          | No                | Ditto. |
-| `bhed` | No                          | No                | Ditto. |
-| `bloc` | No                          | No                | Ditto. |
-| `DSIG` | No                          | No                |        |
-| All other tables | -                 | No                |        |
-
-Please note that OTS library does not parse "unsupported" tables. These
-unsupported tables never appear in a transcoded font.
-
-Supported cmap formats
-----------------------
-
-The following 9 formats are supported:
-
-* "MS Unicode" (platform 3 encoding 1 format 4)
-    * BMP
-* "MS UCS-4" (platform 3 encoding 10 format 12)
-* "MS UCS-4 fallback" (platform 3 encoding 10 format 13)
-* "MS Symbol" (platform 3 encoding 0 format 4)
-* "Mac Roman" (platform 1 encoding 0 format 0)
-    * 1-0-0 format is supported while 1-0-6 is not.
-* "Unicode default" format (platform 0 encoding 0 format 4)
-    * treated as 3-1-4 format
-* "Unicode 1.1" format (platform 0 encoding 1 format 4)
-    * ditto
-* "Unicode 2.0+" format (platform 0 encoding 3 format 4)
-* "Unicode UCS-4" format (platform 0 encoding 4 format 12)
-    * treated as 3-10-12 format
-* Unicode Variation Sequences (platform 0 encoding 5 format 14)
-
-All other types of subtables are not supported and do not appear in transcoded fonts.
-
-Validation strategies
-=====================
-
-With regards to 8 mandatory tables, glyph-related tables (`glyf`, `loca` and `CFF`),
-and hinting-related tables (`cvt`, `prep`, and `fpgm`):
-
-* If OTS finds table-length, table-offset, or table-alignment errors, in other
-  words it cannot continue parsing, OTS treats the error as fatal.
-* If OTS finds simple value error which could be automatically fixed (e.g.,
-  font weight is greater than 900 - that's undefined), and if the error is
-  considered common among non-malicious fonts, OTS rewrites the value and
-  continues transcoding.
-* If OTS finds a value error which is hard to fix (e.g., values which should be
-  sorted are left unsorted), OTS treats the error as fatal.
-
-With regards to optional tables (`VORG`, `gasp`, `hdmx`, `LTSH`, and `VDMX`):
-
-* If OTS finds table-length, table-offset, or table-alignment errors, OTS
-  treats the error as fatal.
-* If OTS finds other errors, it simply drops the table from a transcoded font.
-
-Files
-=====
-
-* include/opentype-sanitiser.h
-    * Declaration for the public API, `ots::Process()`.
-    * Definition of the `OTSStream` interface, a write-only memory stream.
-* include/ots-memory-stream.h
-    * Definition of the `MemoryStream` class which implements the `OTSStream`
-      interface above.
-* src/ots.h
-    * Debug macros.
-    * Definition of a `Buffer` class which is a read-only memory stream.
-* src/ots.cc
-    * Definition of the `ots::Process()` function.
-    * `sfnt` table parser.
-* test/\*.cc
-    * test tools. see test/README for details.
-
-Known issues
-============
-
-Please check the [issues](https://github.com/khaledhosny/ots/issues) page.