diff --git a/docs/hook.md b/docs/hook.md
index e800275..f8bf95b 100644
--- a/docs/hook.md
+++ b/docs/hook.md
@@ -2,38 +2,55 @@
 title: Hook
 ---
 
-### ql.hook_address()
+### Overview
+
+Qiling offers availability of various hooks including access to a address, execution of instructions, interrupts etc. A hook is installed by `ql.hook_*` function series, by offering necessary parameters (e.g. addresses, interrupt numbers) and a callback function, with some optional values:
+
+- `user_data`: any data that will be passed to callback function
+- `begin`: range start of the program counter
+- `end`: range end of the program counter
+(the hook will be triggered when `begin` & `end` are not set or `begin <= program counter <= end` holds true)
+
+When the hook is triggered, the previous callback function will be called with some meta information about this hook (`user_data` is included if provided).
+
+### Usage
+
+##### ql.hook_address(callback, address, user_data=None)
+
+Hook all access to a specific address with the callback form `callback(ql)`.
 
-- hooking a specific address and call a function
 ```python
-    def stop(ql):
-        ql.nprint("killerswtichfound")
-        ql.nprint("No Print")
-        ql.emu_stop()
+def stop(ql):
+    ql.nprint("killerswtichfound")
+    ql.nprint("No Print")
+    ql.emu_stop()
 
+if __name__ == "__main__":
     ql = Qiling(["../examples/rootfs/x86_windows/bin/wannacry.bin"], "../examples/rootfs/x86_windows")
     ql.hook_address(stop, 0x40819a)
     ql.run()
 ```
 
-### ql.hook_code()
+##### ql.hook_code(callback, user_data=None, begin=1, end=0)
+
+Hook all instructions with the callback form `callback(ql, address, size)`.
 
-- hooking every instruction with self defined function
 ```python
 def print_asm(ql, address, size):
     buf = ql.mem.read(address, size)
     for i in md.disasm(buf, address):
         print(":: 0x%x:\t%s\t%s" %(i.address, i.mnemonic, i.op_str))
 
-
 if __name__ == "__main__":
     ql = Qiling(["rootfs/x8664_linux/bin/x8664_hello"], "rootfs/x8664_linux")
     ql.hook_code(print_asm)
     ql.run()
 ```
 
-### ql.hook_block()
-- hooking a block of code
+##### ql.hook_block(callback, user_data=None, begin=1, end=0)
+
+Hook a block of code with the callback form `callback(ql, address, size)`.
+
 ```python
 def ql_hook_block_disasm(ql, address, size):
     ql.nprint("\n[+] Tracing basic block at 0x%x" % (address))
@@ -41,83 +58,133 @@ def ql_hook_block_disasm(ql, address, size):
 ql.hook_block(ql_hook_block_disasm)
 ```
 
-### ql.hook_intno()
+##### ql.hook_insn(callback, type, user_data=None, begin=1, end=0)
 
-- hooking interupt number to invoke a custom fuction
-```python
-ql.hook_intno(hook_syscall, 0x80)
-```
+Hook specific instructions by `type` with callback form `callback(ql)`.
 
-### ql.hook_insn()
+The `type` indicates the instruction type. It should be among `UC_X86_INS_IN`, `UC_X86_INS_OUT`, `UC_X86_INS_SYSCALL`, `UC_X86_INS_SYSENTER`.
 
-- hooking specific interupt number to invoke a custom fuction
 ```python
-ql.hook_insn(hook_syscall, UC_X86_INS_SYSCALL)
-```
+from unicorn.x86_const import *
 
+def on_syscall(ql):
+    print("Doing syscall by x86 SYSCALL instruction.")
 
-### ql.hook_int()
-- interupt
-```python
-ql.hook_intr()
+ql.hook_insn(on_syscall, UC_X86_INS_SYSCALL)
 ```
 
-### ql.hook_mem_unmapped()
-```python
-```
+##### ql.hook_intno(callback, intno, user_data=None)
 
-### ql.hook_mem_read_invalid()
-```python
-```
+Hook specific interrupts by `intno` with callback form `callback(ql, intno)`.
 
-### ql.hook_mem_write_invalid()
 ```python
-```
+def on_syscall(ql, intno):
+    print("Doing syscall by int 0x80.")
 
-### ql.hook_mem_fetch_invalid()
-```python
+if __name__ == "__main__":
+    ql = Qiling(["rootfs/x86_linux/bin/x86_hello"], "rootfs/x86_linux")
+    ql.hook_intno(on_syscall, 0x80)
+    ql.run()
 ```
 
-### qll.hook_mem_invalid()
-```python
-```
+##### ql.hook_intr(callback, user_data=None, begin=1, end=0)
 
-### ql.hook_mem_read()
+Hook all interrupts with callback form `callback(ql, intno)`.
 
-- monitoring a process performing memory read on a specific address
 ```python
-def _mem_read(ql, addr, size, value):
-    print("demo for ql.hook_mem_read")
+def on_interrupt(ql, intno):
+    print("Interrupt number %x" % (intno))
 
-ql.hook_mem_read(_mem_read, 0xffffdef4)
+if __name__ == "__main__":
+    ql = Qiling(["rootfs/x86_linux/bin/x86_hello"], "rootfs/x86_linux")
+    ql.hook_intr(on_interrupt)
+    ql.run()
 ```
 
-### ql.hook_mem_write()
+##### ql.hook_mem_invalid(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_valid(callback, user_data=None, begin=1, end=0)
+
+Hook valid / invalid access to memory with callback form `callback(ql, access, address, size, value)`. An invalid access includes unmapped, protected memories
+
+Callback parameter `access` is a value in `uc_mem_type` to indicate the access type:
+  - `UC_MEM_READ`: normal read from the memory (valid)
+  - `UC_MEM_WRITE`: normal write to the memory (valid)
+  - `UC_MEM_FETCH`: normal fetch of the memory (valid)
+  - `UC_MEM_READ_UNMAPPED`: read from unmapped memory (invalid)
+  - `UC_MEM_WRITE_UNMAPPED`: write to unmapped memory (invalid)
+  - `UC_MEM_FETCH_UNMAPPED`: fetch of unmapped memory (invalid)
+  - `UC_MEM_WRITE_PROT`: write to protected memory (invalid)
+  - `UC_MEM_READ_PROT`: read from protected memory (invalid)
+  - `UC_MEM_FETCH_PROT`: fetch of protected memory (invalid)
+  - `UC_MEM_READ_AFTER`: post-read from the memory (valid)
 
-- monitoring a process performing memory write on a specific address
 ```python
-def _mem_write(ql, addr, size, value):
-    print("demo for ql.hook_mem_read")
+def on_mem_valid(ql, access, address, size, value):
+    print('Valid access', access, address, size, value)
 
-ql.hook_mem_write(_mem_write, 0xffffdef4)
-```
+def on_mem_invalid(ql, access, address, size, value):
+    print('Invalid access', access, address, size, value)
 
-### ql.hook_mem_fetch()
+    PAGE_SIZE = ql.mem.pagesize
+    aligned = ql.mem.align(address)
 
-- monitoring a process performing memory fetch on a specific address
-```python
-def _mem_fetch(ql, addr, size, value):
-    print("demo for ql.hook_mem_read")
+    ql.mem.map(aligned, PAGE_SIZE)
+    ql.mem.write(aligned, b'Q' * PAGE_SIZE)
 
-ql.hook_mem_fetch(_mem_write, 0xffffdef4)
+if __name__ == "__main__":
+    ql = Qiling(["rootfs/x8664_linux/bin/mem_invalid_access"], "rootfs/x8664_linux")
+    ql.hook_mem_invalid(on_mem_invalid)
+    ql.hook_mem_valid(on_mem_valid)
+    ql.run()
 ```
 
-### ql.hook_del()
+##### ql.hook_mem_read(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_write(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_fetch(callback, user_data=None, begin=1, end=0)
+
+Hook specific types of *valid* memory access with callback form `callback(ql, access, address, size, value)`.
+
+Different methods limit the memory access types (callback `access`) to:
+- `ql.hook_mem_read`: all valid reads (`UC_MEM_READ`)
+- `ql.hook_mem_write`: all valid writes (`UC_MEM_WRITE`)
+- `ql.hook_mem_fetch`: all valid fetches (`UC_MEM_FETCH`)
+
+Usages are similar to `ql.hook_mem_valid`.
+
+##### ql.hook_mem_unmapped(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_read_invalid(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_write_invalid(callback, user_data=None, begin=1, end=0)
+##### ql.hook_mem_fetch_invalid(callback, user_data=None, begin=1, end=0)
+
+Hook specific types of *invalid* memory access with callback form `callback(ql, access, address, size, value)`.
+
+Different methods limit the memory access types (callback `access`) to:
+- `ql.hook_mem_unmapped`: all unmapped access (`UC_MEM_READ_UNMAPPED | UC_MEM_WRITE_UNMAPPED | UC_MEM_FETCH_UNMAPPED`)
+- `ql.hook_read_invalid`: all invalid reads (`UC_MEM_READ_UNMAPPED | UC_MEM_READ_PROT`)
+- `ql.hook_mem_write_invalid`: all invalid writes (`UC_MEM_WRITE_UNMAPPED | UC_MEM_WRITE_PROT`)
+- `ql.hook_fetch_invalid`: all invalid fetches (`UC_MEM_FETCH_UNMAPPED | UC_MEM_FETCH_PROT`)
+
+Usages are similar to `ql.hook_mem_invalid`.
+
+##### ql.hook_del(hook_ret)
+
+Delete a hook. Parameter `hook_ret` is the return result of a `ql.hook_*` function.
+
 ```python
+def hook_syscall(ql, intno):
+    print("Doing syscall by int 0x80.")
+
+if __name__ == "__main__":
+    ql = Qiling(["rootfs/x86_linux/bin/x86_hello"], "rootfs/x86_linux")
+    hook_ret = ql.hook_intno(hook_syscall, 0x80)
+    ql.hook_del(hook_ret)
+    ql.run()
 ```
 
-### ql.clear_hooks() 
-- clear all hooks
+##### ql.clear_hooks()
+
+Remove all installed hooks.
+
 ```python
 ql.clear_hooks()
 ```