update syntax docs

1 files changed, 242 insertions, 1 deletions

diff --git a/guide/syntax_description.md b/guide/syntax_description.md
index 66e96dcc..63bd8373 100644
--- a/guide/syntax_description.md
+++ b/guide/syntax_description.md
@@ -9,6 +9,187 @@ target("test")
     add_files("src/*.c")
 ```
 
+## Configuration Separation
+
+Xmake.lua uses the 28th principle to implement a two-layer separate configuration of the description domain and the script domain.
+
+What is the 28th principle? In short, most of the project configuration, 80% of the cases, are basic basic configurations, such as: `add_cxflags`, `add_links`, etc.
+Only less than 20% of the space needs to be extra complex to meet some special configuration needs.
+
+The remaining 20% of the configuration is usually more complicated. if it is directly flooded in the whole xmake.lua, the whole project configuration will be very confusing and very unreadable.
+
+Therefore, xmake isolates 80% of simple configuration and 20% of complex configuration by describing two different configurations of domain and script domain, making the whole xmake.lua look very clear and intuitive, readable and maintainable. Get the best.
+
+### Description Scope
+
+for beginners who are just getting started, or just to maintain some simple small projects, the requirements are fully met by describing the configuration completely. What is the description domain? It looks like this:
+
+```lua
+target("test")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("DEBUG")
+    add_links("pthread", "m", "dl")
+```
+
+At first glance, it is actually a configuration set of `set_xxx`/`add_xxx`. for the novice, you can not use it as a lua script, just as an ordinary, but there are some basic rules configuration files.
+
+if, by looking, there are parentheses, or function calls like scripting languages, then we can also write this (whether with parentheses to see personal preferences):
+
+```lua
+target "test"
+    set_kind "binary"
+    add_files "src/*.c"
+    add_defines "DEBUG"
+    add_links "pthread", "m", "dl"
+```
+
+Is this looking more like a profile? In fact, the description field is a configuration file, similar to the configuration of keys/values such as json, so even if you are not a newcomer to lua, you can quickly get started.
+
+Moreover, for the usual projects, only the various settings of the project are configured by `set_xxx/add_xxx`, which has fully met the requirements.
+
+This is what I said at the beginning: 80% of the time, you can use the simplest configuration rules to simplify the configuration of the project, improve readability and maintainability, so that users and developers will be very friendly and more intuitive.
+
+What if we want to make some conditional judgments for different platforms and architectures? It doesn't matter, the description field is in addition to the basic configuration, it also supports conditional judgment, as well as the for loop:
+
+```lua
+target("test")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("DEBUG")
+    if is_plat("linux", "macosx") then
+        add_links("pthread", "m", "dl")
+    end
+```
+
+```lua
+target("test")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("DEBUG")
+    for _, name in ipairs({"pthread", "m", "dl"}) do
+        add_links(name)
+    end
+```
+
+Is this looking a bit like lua? Although, it can usually be regarded as a common configuration problem, but xmake is based on lua after all, so the description domain still supports the basic language features of lua.
+
+!> However, it should be noted that although the description field supports lua script syntax, try not to write too complicated lua scripts in the description field, such as some time-consuming function calls and for loops.
+
+And in the description field, the main purpose is to set the configuration item, so xmake does not completely open all module interfaces, many interfaces are forbidden to be called in the description field.
+Even open callable interfaces are completely read-only, and time-consuming security interfaces such as `os.getenv()` read some general system information for configuration logic control.
+
+!> Also note that xmake.lua is parsed multiple times to resolve different configuration fields at different stages: for example: `option()`, `target()`, etc.
+
+So, don't think about writing complex lua scripts in the description field of xmake.lua, and don't call print in the description field to display the information, because it will be executed multiple times, remember: it will be executed multiple times! ! !
+
+### Script Scope
+
+Restrict the description field to write complex lua, all kinds of lua modules and interfaces are not used? How to do? This time is the time for the script domain to appear.
+
+if the user is already fully familiar with xmake's description domain configuration and feels that some of the special configuration maintenance on the project is not met, then we can do more complex configuration logic in the script domain:
+
+```lua
+target("test")
+    set_kind("binary")
+    add_files("src/*.c")
+    on_load(function (target)
+        if is_plat("linux", "macosx") then
+            target:add("links", "pthread", "m", "dl")
+        end
+    end)
+    after_build(function (target)
+        Import("core.project.config")
+        Local targetfile = target:targetfile()
+        Os.cp(targetfile, path.join(config.buildir(), path.filename(targetfile)))
+        Print("build %s", targetfile)
+    end)
+```
+
+As long as it is similar: `on_xxx`, `after_xxx`, `before_xxx`, etc. The script inside the function body belongs to the script field.
+
+In the script domain, the user can do anything, xmake provides an import interface to import various lua modules built into xmake, and can also import user-supplied lua scripts.
+
+We can implement any function you want to implement in the script domain, even if you write a separate project.
+
+for some script fragments, it is not very bloated, such as the above built-in writing is enough, if you need to implement more complex scripts, do not want to be filled in a xmake.lua, you can separate the script into a separate lua file for maintenance.
+
+E.g:
+
+```lua
+target("test")
+    set_kind("binary")
+    add_files("src/*.c")
+    on_load("modules.test.load")
+    on_install("modules.test.install")
+```
+
+We can place the custom scripts in the corresponding directory of xmake.lua, and maintain them independently in `modules/test/load.lua` and `modules/test/install.lua`.
+
+In these independent lua scripts, we can also import various built-in modules and custom modules through [import](/zh-cn/manual/builtin_modules?id=import), just like to write lua, java is no different. .
+
+for the different stages of the script's domain, `on_load` is mainly used for target loading, do some dynamic configuration, not like the description field, it will only be executed once!!!
+
+In other stages, there are many, such as: `on/after/before`_`build/install/package/run`, etc. See the target api manual section later, so I won’t go into details here.
+
+## Configuration Type
+
+In the description domain configuration, you can configure the configuration fields and configuration items. In the configuration domain, you can configure various configuration items through the interface of `set_xxx`/`add_xxx`.
+
+```lua
+target("test1")
+    set_kind("binary")
+    add_files("src/*.c")
+
+target("test2")
+    set_kind("binary")
+    add_files("src/*.c")
+```
+
+In the above configuration, the target belongs to the configuration domain, and all the `set_xx`/`add_xxx` interface configurations below it belong to the configuration item, which is partially effective for this target.
+
+We can understand it as a local scope, similar to the block block in c:
+
+```
+target("test1")
+{
+    set_kind("binary")
+    add_files("src/*.c")
+}
+target("test2")
+{
+    set_kind("binary")
+    add_files("src/*.c")
+}
+```
+
+However, in order to simplify the writing, xmake stipulates that each newly defined target field starts, and the last configuration field ends automatically. Of course, if the user feels troubled, you can manually configure the leaving domain:
+
+
+```lua
+target("test1")
+    set_kind("binary")
+    add_files("src/*.c")
+target_end()
+
+target("test2")
+    set_kind("binary")
+    add_files("src/*.c")
+target_end()
+```
+
+### Configuration Scope
+
+Currently available configuration scopes are: `target()`, `option()`, `task()`, `package()`
+
+for a detailed description of each domain, see: [API Manual](/manual/project_target)
+
+### Configuration Item
+
+As long as the configuration with the words `set_xxx` and `add_xxx` is a configuration item, multiple configuration items can be set in one configuration field.
+
+for a description of the configuration items, see: [Interface Specifications](/manual/specification)
+
 ## Scope
 
 The description syntax of xmake is divided by scope, which is mainly divided into:
@@ -200,7 +381,7 @@ target_end()
 
 Call `option_end()`, `target_end()` to explicitly leave the current target/option field setting.
 
-### Scope indentation
+### Scope Indentation
 
 Indentation in xmake.lua is just a specification for more clear distinction. The current setting is for that scope, although it is ok even if it is not indented, but it is not very readable. .
 
@@ -226,6 +407,66 @@ Therefore, proper indentation helps to better maintain xmake.lua
 
 Finally attached, tbox's [xmake.lua](https://github.com/tboox/tbox/blob/master/src/tbox/xmake.lua) description, for reference only. .
 
+## Multi-level Configuration
+
+In the script field we can import various rich extension modules by import, and in the description field we can introduce the project subdirectory through the [includes](/#/zh-cn/manual/global_interfaces?id=includes) interface. The xmake.lua configuration.
+
+Remember: xmake's includes handles the configuration relationship according to the tree structure. The target configuration in xmake.lua in the subdirectory inherits the root domain configuration in the parent xmake.lua, for example:
+
+Currently there are the following project structures:
+
+```
+Projectdir
+    - xmake.lua
+    - src
+      - xmake.lua
+```
+
+`projectdir/xmake.lua` is the project's root xmake.lua configuration, and `src/xmake.lua` is a sub-configuration of the project.
+
+`projectdir/xmake.lua` content:
+
+```lua
+add_defines("ROOT")
+
+target("test1")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("TEST1")
+
+target("test2")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("TEST2")
+
+Includes("src")
+```
+
+The global root domain is configured with `add_defines("ROOT")`, which affects all target configurations below, including all target configurations in the sub-xmake.lua of includes, so this is the global total configuration.
+
+The `add_defines("TEST1")` and `add_defines("TEST2")` in test1/test2 belong to the local configuration and only take effect on the current target.
+
+`src/xmake.lua` content:
+
+```lua
+add_defines("ROOT2")
+
+target("test3")
+    set_kind("binary")
+    add_files("src/*.c")
+    add_defines("TEST3")
+```
+
+In the `src/xmake.lua` sub-configuration, there is also a global root domain, configured with `add_defines("ROOT2")`, which belongs to the sub-configuration root domain and only takes effect on all targets in the current sub-xmake.lua. For the target xmake.lua in the lower level includes the target, because previously said, xmake is the configuration inheritance relationship of the tree structure.
+
+Therefore, the final configuration results of these targets are:
+
+```
+target("test1"): -DROOT -DTEST1
+target("test2"): -DROOT -DTEST2
+target("test3"): -DROOT -DROOT2 -DTEST3
+```
+
 ## Syntax simplification
 
 The configuration field syntax of xmake.lua is very flexible and can be used in a variety of complex and flexible configurations in the relevant domain, but for many streamlined small block configurations, this time is slightly redundant: