Step 1:  root cause of the CWE-476 (NULL Pointer Dereference) vulnerability in the given code slice is:

The code attempts to access the 'type' member of 'content->c1' without first checking if 'content->c1' is NULL. This can lead to a NULL pointer dereference if 'content->c1' is indeed NULL.

The vulnerability occurs because:

1. The function checks if 'content' is NULL at the beginning (line 3), but it doesn't check if 'content->c1' is NULL before accessing it.

2. The code assumes that if 'content' is not NULL, then 'content->c1' will also be valid, which may not always be the case.

3. There's no defensive programming to ensure that 'content->c1' is not NULL before attempting to access its 'type' member.

To fix this vulnerability, a NULL check should be added for 'content->c1' before accessing its members. This would prevent the potential NULL pointer dereference and make the code more robust.
Step 2. Here are five possible patches to fix the CWE-476 vulnerability:

Patch 1: Add a NULL check for content->c1 before accessing it
```
<     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
---
>     if (content->c1 != NULL && (content->c1->type == XML_ELEMENT_CONTENT_OR) ||
```

Patch 2: Use a separate if statement to check for NULL
```
<     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
---
>     if (content->c1 == NULL) return;
>     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
```

Patch 3: Use a ternary operator to handle NULL case
```
<     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
---
>     if ((content->c1 ? content->c1->type : 0) == XML_ELEMENT_CONTENT_OR ||
```

Patch 4: Use a macro for safe access
```
< #define SAFE_ACCESS(ptr, member) ((ptr) ? (ptr)->member : 0)
< ...
<     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
---
> #define SAFE_ACCESS(ptr, member) ((ptr) ? (ptr)->member : 0)
> ...
>     if ((SAFE_ACCESS(content->c1, type) == XML_ELEMENT_CONTENT_OR) ||
```

Patch 5: Use a helper function for safe access
```
< static int safe_get_type(xmlElementContentPtr ptr) {
<     return ptr ? ptr->type : 0;
< }
< ...
<     if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
---
> static int safe_get_type(xmlElementContentPtr ptr) {
>     return ptr ? ptr->type : 0;
> }
> ...
>     if ((safe_get_type(content->c1) == XML_ELEMENT_CONTENT_OR) ||
```

Each of these patches addresses the vulnerability by ensuring that content->c1 is not NULL before accessing its type member, thus preventing a potential NULL pointer dereference.